Having a video card with tons of horsepower and two monitor headers has proven to be too much to resist. We've long thought about having a 21" monitor, and now we've done. The Red-Dragon now has as it's primary monitor, a 21" `Perfect Flash' ViewSonic running in 2048x1536 at 68 Hz. Our 19" Schneider sites along side, running 1600x1200 at 75 Hz. With 3.1 megapixels, the 21" ViewSonic is an awesome graphics monitor. And with the additional space from a second desktop on the 19", we have tons of needed workspace.
We typically setup the 19" as a status space, watching the web server logs, bandwidth and temperatures, along with holding some standard apps, like the IM list and music. When work with graphics, the 21" holds the image, while the 19" holds tools like layers, color palette and the like. It is an excellent setup :)