It's a spacious concept, but to be brutally honest, I'm not too thrilled with the drawing room concept right in the front door. (I use rooms in nontraditional ways, but not everyone is unconventional.) I'm not a fan of eating dinner where I can see the kitchen mess. I'd move the dining room to the foyer. Center a table with whatever chandelier would be impressive, keep chairs against hte walls (flanking matching floating buffets) until needed, except for 2 grand chairs (wingbacks?). Where that line is drawn across the "foyer" is what? THere's the option of something dramatic along that line to separate "foyer" from the rest: dramatic silk draperies that puddle; Morrocan wood screen that folds back, stained glass or clear beveled glass panels suspended between floor and ceiling. A lot of this will depend on whether you have pets, children.

That leaves the current dining area as "breakfast nook"

I am not clear enough on the flow of the house to make any suggestions. What door would be the entry for guests? and would that be the same door family uses?
Of course you could opt to close in the stairs next to the dining room, and I think that would be a good idea.
You could also close in the kitchen, either on both sides, or just one, by putting a door (swinging would make the most sense) between dining and kitchen and having cabinets to the ceiling (I can't tell if they are already, though it does seem like the fridge is there, which would be strange if it is only bottom cabinets).
You could also opt not to have bar seating, and have cabinets to ceiling from kitchen to living also. This would really close in your space (especially the kitchen), and you have to decide how you use the space and what you love and don't love about the different ideas.
Another way to create a visual separation between the living and dining room would be with hanging lights over the bar/seating area. Perhaps something you have planned already, but if they are substantial in size they will create a distinction between the spaces.
Or you could have the open shelves which used to be more popular, but in my opinion they fell out of style for good reasons. However, it might work for you.
On the drawing room I would probably opt to close it in with frosted french doors, or not frosted, whatever. If you choose sliding/pocket doors you can still opt for the open concept if ever the fancy strikes you.

I am a bit confused as to the use of the Drawing Room - will this be used by the family or is it only a very formal room for guests? The first thing I would do would be to add some kind of a pierced wall, resin panels ( http://www.lumicor.com/) or architectural screen in the center of the 'back' of the room (between the drawing room and the stairs and dining room). This would allow you to center your furniture in the center, with the traffic patterns to the left and right, as well as giving you a focal point when you walk into the house. If it is really important to you to keep it open, then use a half wall with pendant fixtures over it. Even with this, you might want to still install a full height portion in the middle and put some artwork on it as your focal point. This would also draw the eye into the house and entice you to look behind that wall. Otherwise, you see almost everything at the same time. The plan as shown makes me think of a hotel lobby, with the furniture placed against the walls (too far apart for conversation, plus the traffic pattern goes right through it)

The other problem I see is the dining room - you only have 8 feet in width, which is VERY small. Assuming you use a 36"w table, that only leaves you 30" on either side of the table, which is not enough room for chairs and circulation. The easiest fix I see to this, given the dimensions, would be to change the kitchen layout. I would make this a u-shape, open to the dining side, i.e. attach the breakfast bar to the range wall. You could extend your cabinetry on the back outside wall, approximately as far as where the current cabinets are shown. Your refrigerator could go on this back wall, the sink on the breakfast bar wall (raise the bar to 42"H and extend 12+") This makes your dining room less formal, but it makes it useable - a better trade-off - and since it is your only table area, I would think that this would be fine.

I just did a reno on my living/kitchen room. This is the result
http://www.houzz.com/projects/11743/Living-and-Kitchen-Reno
I'm a fan of using ceiling detail to help define different spaces. In my room I used a ceiling 'grid' and hanging lights in different areas to make them separate and different.
This space for us was just as open before BUT they had visual blocks with kitchen cabinets - this was very irritating and ruined the space.

You are smart to be asking for input now. I can only offer some opinions from my own personal & professional experience. I agree with comments above that open is good to a point, but when I have a dinner party I am not the type to do the dishes right away, I want to enjoy my company & I don't want to be looking at them.
From a feng shui perspective, having an entry that is not open to the house is important. When I am staging, I will use screen/room divider to keep entry separate space. I don't want people who come to my door, who I may not know, being able to look into my home. I also prefer a cozy place for reading, which wide open space may not allow.

To create a cozy feel perhaps consider placing 4' walls and create an arch way in the living room and another in the drawing room. You can leave yourself 6' clearance to transition from one room to the next. You can design a niche wall by the entrance and place a beautiful arrangement of fresh flowers or live plant creating a focal point but leaving yourself 2'6" clearance from the door. The wow element can be created by enhancing the stair case area with floaters cables. Make the stairs a conversation piece a sculpture. Have FUN!

I have a very similar floor plan to yours except the door enters the room on the opposite side of the home and we have a foyer at the entry. Columns frame in the dining area (which we've converted to a library) and where you have your living room we've changed to a breakfast room where it overlooks the screened porch except we eat all of our meals there now that we don't have a dining room. We have no interior walls between the breakfast room and the "great room" .... What you call your drawing room. I like the openness and the columns and singular wall in the former dining room separates the foyer from the man living area. You can see our floor plan at stephenfuller.com but we made swveral modifications. Stephen's Walk is the name of the houseplan. Good luck!

DON'T close it in! My entry, LR, DR and stairs are all open and everyone who enters gives a big "WOW"! They all love the openness of it, and it definitely makes everything look much larger. I do have a couple of steps down to the living room. I love inkwitch's idea of putting your dining room where the drawing room is currently indicated. The silk draperies pulled back to the columns under the arch would be dramatic and offer an "eye break". As for the kitchen mess, just raise the kitchen bar 6-8 inches above the counter and use high bar chairs. It will block the view of your countertop.

I like the floor plan as it is. I would suggest rearranging the furniture in the living room to have the back of the couch facing the kitchen and the two chairs opposite the couch facing it. Pulling the furniture off of the walls will help make the place feel cozier, and the room feel larger at the same time. I also think that by putting the dining table in the drawing room area will help split up that space a bit. You could do half dining room, half entryway-type area. Also putting faux columns up in the drawing room area (maybe 4 in a 4'x4' square, right in the middle) could help visually separate that space. Once the furniture is placed, and the pendant lights are hanging down, the room will feel well defined. Can't wait to see it finished!

I would make the Drawing room into a grand foyer...definitely don't turn it into the dining room. You wouldn't want to walk in the front door through the dining room. I love an open concept and think once you got all of your furnishings in it you wouldn't feel like it is too open.

One possibility would be to swap the living room and the dining room. Since the current living room is larger than the current dining room you could still keep some comfortable seating (couch and upholstered chairs?) against the front wall for a keeping room/dining concept. Then your new dining areas (kitchen and dining room) and living areas (living and drawing room) would have good flow between them, which would work well both for family and entertaining. You could also add some builtin bookshelves in the drawing room or new living room to create a library area to add another fun element to the living areas. These bookshelves could be against the long walls in the drawing room, around the window with a window seat in the living room (former dining room), or built to create some separation in the open area between the drawing room and living room/stair area. Your plan seems to show some sort of builtin there, but I'm not sure what it is.

Thanks to all who replied and suggested so many thing. Just to clear some of your doubts : Drawing room is for formal entertainment and will be rarely used. I have decided to put buttcherd glass of about 3 feet on both sides where u see the dotted line and this will be done with plywood, and can be used as display unit. It will partialy cover my stairs and dining room and still give a feel of openess. I am going to move the seating in the same room to left side of the wall and use the other wall to hang big mirror or painting witha nice table.
2. Living room will be for family and will have TV unit there. Bar stools are for breakfast nook. Dining room will be used for family dinners and lunches. The door near the parking will be used by maids and other service.

I will definetely post a photo once the project is over. which will take about 4 to 5 months so may be by August 2011 it should be done.