I had a Samsung 24" 1920x1200 (16:10) 5 milliseconds for about 2 years.
Two months ago, I switched to a Asus 27" 1920x1080 (16:9) 2milliseconds.
The reason was that I wasn't happy with the bluriness of my screen, when I moved the mouse. The picture was nice if I held the mouse/camera still. But when moving, I just didn't like what I saw. I thought that this was because of the 5 millisecond delay of my screen. I hoped that a 2 millisecond screen would make the picture more clear when moving. I didn't know for sure, and you can't check when buying over the Internet. So I took the jump, and bought a new monitor.
The screen is indeed a bit less blurry when I move. But not much. It probably wasn't worth the money.
I do miss my 16:10 monitor, and the extra pixels. But only when on the desktop. In games, it doesn't matter. Although maybe 16:9 gives a more "natural" view. I don't play WoW anymore, but when I did, the vertical height was very important, because I ran a heavily modified UI. I played a month of Guild Wars 2 (didn't like it in the end), but there I didn't miss the extra height for my UI.
I do like the fact that my new monitor is 27". The pixels/centimeter is of course lower, but you don't notice that in games. (On the desktop, text is a bit more "grainy" then on my old monitor). I think 27" is the max I want in screensize. At least when the monitor stand on my desk, and the distance to my eyes is 50-60 cm (2 feet).
A good side-effect is the fact that in demanding games, my framerates really went up 10% ! The fact that you have 10% less pixels indeed causes linear higher framerates. This is the reason I will not switch to 2560x1440 or 2560x1600 for a few more years. With 2560x1600 I expect a 50% drop in framerates (2m versus 4m pixels). Too high for me.
So for now, I'll keep using my 1920x1080, 2ms, 27" screen.
One of my real-life friends (who is also a gamer) has a 23" 8 millisecond 1080p IPS screen. For some reason, his screen seems less blurry when he moves the camera. It might be worthwile to consider an IPS screen. That would be easier if you could compare screens side-by-side somewhere.
What I'd really like:
1) IPS technology
4) 2 ms delay
5) 120 Hz
6) not too expensive
So far it looks like nothing is coming close, even if you have a high budget.