I used to run a 17" Sony CRT and I recently upgraded to a 21" FPD2185W Widescreen LCD from Gateway.
My entire PC experience has been changed by the 1680X1050 resolution, and I would never go back to anything smaller in screen size, nor lower in resolution.
I can fit all of my toolbars on the screen in WoW with no issues, and I can see more of the play field than I could in the past. Did you know the bottom toolbars have little dragon "bookends" that you can't see with 4:3?
I also use Photoshop, and this monitor is a champ for this application. I can see many more layers than before and everything looks crisp and clean.
Movies...that is obvious.
The transition to a widescreen monitor was easy for me because I have a 46" Widescreen TV as well, and I just bought the wife a 19" Widescreen LCD for her PC, so I have moved away from 4:3 in my home completely.