I myself use a widescreen monitor (Acer 1916LW i think, 16:10 ratio) and it is truely brilliant. Playing counter-strike:source feels like you're in a movie. Games like Black & White 2 take on a whole new epic scale.

Unfortunately older games aren't compatible with widescreen resolutions (they use old skool 4:3 ratio), and for some reason the occasional modern game comes out where the developers have forgotten about widescreen, Prey is a good example. I have to run it in 1024x786 resolution, which makes things look a bit pixelated.

But i definitely recommend a widescreen monitor. The pros outweigh the cons by a gigantic amount.

Plus, if you use a tabbed internet browser like Opera, you can fit more tabs on screen!