Honestly, for a bedroom only game monitor I would go with 32", the advantage being the smallish size making pixels hard to notice but the screen not being so small objects in the playfield are hard to notice. Good balance.
If you watch widescreen movies, I would say about 60-80" due to half of the screen size being wasted on black bars. (I fucking hate widescreen movies for that reason but that's another rant for another day)
While distance and such does matter I should also mention some TVs do some nice additional upscaling and although I still hold most people probably will not benefit from "HD" the extra resolution as a feeder for upscaling and such is quite nice. Now this probably will not work for games (it is the reason for the game mode on TVs) and you will probably have to part with a pretty penny for a TV with such abilities
Also as I have not done it for a while- plug for projectors. Some of the LED ones are awesome these days with thousands of hours of lifetime so no real need to worry about finding a silly bulb every couple of months.
Is it still possible to buy 720p TVs these days ? Everywhere I look I see only 1080p led TVs, with a ton of shitty add-ons that I don't really need when all I want to do is play Wii games on it ! Internet, 3D, eco-solution and so on, are just another useless reason to make you pay more and shop for a brand new TV.
I'm sure my Wii would look better on a cheap 720p TV if i could find one, but instead I had to get a quite expensive 1080p Samsung LED TV !!
Anyway, I'm sure I'll enjoy my TV set to the fullest when I'll get the Wii U, or whatever it'll be called.
For the original question, for my gaming systems I decided to go with a 22" TV.
Small , isn't it ? The reason is that originally I was a PC gamer, and I was used to play games on my 22" monitor, at night , on my desk ( fairly close to the monitor ) and with headphones on. The effect was a totally immersion in the game. I felt I was living inside of the game when I was playing the original Bioschock , Batman AC and any COD game.
Now my PC is sadly gone, so I decided to buy a small TV instead ( with all the connections that my monitor didn't have, like component, composite,s-video, VGA, HDMI ) so I can play console games on it just like I used to play PC games. And it works fairly well for Wii games, because the screen is so small, games look somehow sharper on it.
But that's my personal preference.
If I had a bigger room and some more space, I would go with a 40" TV, so that the level of ' immersion ' would be the same even sitting on a couch a few feet away.
Yes, I know that.
I'm just saying that with less upscaling to deal with ( 480p to 720p instead of 480p to 1080p ) you could end up with a better image.
Besides, I remember my old PC looked just fine on my 1024x 768 monitor native resolution, now if I wanna play a game at 1024x768 on a 1080p display I get a less then optimal image( ugly actuallly ).
The higher the native resolution of a display, the uglier low res images are gonna look on it.