I play 9, tiled. 22" though, in 1600x1200. 20" might become a bit small. Like this:
Only now I just started using AHK scripts to remove the titlebars, so I have a bit more space. And for keyboard control, since my wrist is starting to hurt from using the mouse too much.
The title bar removal doesn't help that much, actually, since I have a 4:3 screen; however, if you are using a widescreen it will help a lot. I'm thinking of that 24" samsung widescreen.