2 of my friends have 32" hd tv's as their monitors.. both think it is the perfect size, although one of them just for multitasking, wall mounted it and uses for gaming, whilst having another 3 22" screens underneath all in 1920x1200
I was going to go for a 32" but on the day was like 'stuff it' (just not using those words), as my money had been delayed for buying one i was a bit annoyed, I just went into the shop and thought I would risk a 37", I'm not complaining, but it could do with being a bit lower, or my chair higher.. but then the chair is limited by the keyboard slide out shelf. I think a 32" would also be good, I'm only about 3 feet away and use it as my primary monitor for about 4 hours a day or up to even 13 on a weekend, I find it better for my slightly bad eyesight than a smaller screen, and I am now used to it, and other people see it and are like WOE!, but I'm just used to it now, I could fit a bigger screen like 42" into my range of view but wouldn't really want to. I'm thinking 32" roughly is pretty damn nice for most people, but I am not personally regretting the extra 5 inches, even though the resolution is the same.. it's still not bad, and still awesome for gaming... but at first I got motion sickness from portal lol...
Most say 24" is perfect, but I think if you put a 28" infront of them for a few weeks then they would say that is perfect, and same for up to 32" unless it's way too close, and my 37" might be a bit overkill, although there are people with 40" and 42" setups on these forums, but they tend to find it a bit big as a main screen.. I don't think I could go under 32" now, unless I had multi monitors.. but I think I prefer 1 big one for games, any extras (which I will get) are for multitasking.