Crazy to see this posted.  I was just complaining about this yesterday.  I have a 55 LCD upstairs and when my wife is at work and I am watching the kids I play on that.  My couch is pretty far away as the tv is on the fireplace and I get my ass handed to me and am little more then a moving target.  I rarely go positive and it is merely for points.  In my basement I have my old college 36" standard def and I sit directly in front of it.  36" widescreen isnt that big but being standard def it is big.  My gun accuracy on my standard def is literally probably 10% higher and my kdr probably goes up over 1/2 a point compared to the big one.

We also have a 32" widescreen at the firehouse and the times I play there are also horrible.  The sway side to side is jittery and I have to lower my sensetivity down by 2.  I take the standard def tvs anyday but Im sure if I had started on a widescreen I would feel different.  Ina game of reflexes and milliseconds consistancy is key I think.

I play on the 8" I plug into my truck with the bunny ears attached !

Definitely, yes. Smaller screens will always have the advantage of seeing everything at once over the person traveling from all four corners with a larger screen.

Also, high-definition obviously beats standard-definition because of brightness and contrast pluses. And I've noticed that even on-screen text is hard to read on some games using a standard-definition television (try dead rising on a standard t.v. and you'll see how horrible this is).

BRIGHTNESS TIP: Whenever a game asks you to adjust the brightness to a certain level for maximum quality, ignore it, and set the brightness to full. Helps with those dark levels a lot (this is obvious, but a lot of people don't seem to take advantage of it).

I've recently downgraded from HD to SD as I recently aquired a cheap Xbox and wanted to use my over-the-head headset with it. To be honest, my skill hasn't decreased and you don't notice much of a quality drop. However when I go back up to HD, on my PS3, it seems really futuristic.

In my living room - 110"  1080 HD projector, projected to a +2 screen (+2 means that it has glass beads shot onto the screen to increase the sharpness)
In my bedroom - 42" 1080 LCD
In my 2nd bedroom - 32" 1080 LED

In the living room I sit about 18 feet away from screen, lights out, no need to move head to see everything.

In the bedroom I sit about 6 feet away from screen, ambient to no light, no need to move head to see everything.

In the 2nd bedroom I sit about 3 feet away from screen, no light (LED has deeper blacks and light messes up the dark areas of the maps), no need to move head to see everything.

I do have great peripheral vision so maybe that helps also.

People who come and play on my big screen say that it takes time to get adjusted to the size. I have had a projector as my main 'tv' (various brands) for the past 10 years or so. I am used  to playing on that big of screen.