I've used VNC (and variations of it, Tight / Ultra / etc etc) for a very long time now - from back in the days when PCanywhere for Windows was quite expensive and considered quite an elaborate product, but you needed to use it because it supported IPX/SPX (eeek). I still have versions of VNC installed on a couple of servers at work, but that's all going to change, because now that the first Windows 2003 servers are starting to be deployed here, I've started learning to really appreciate the power of the Windows Remote Desktop.
I was initially wary of it, and when I tested it with Windows 2000 it wasn't as impressive as it is now, but in 2003 / XP it has enough of a level of integration to make me never want to put up with VNC's random crashes, redrawing errors/delays, lack of functionality again.
Why Remote Desktop >>> VNC
OS Integration
Use your existing domain / computer security database and allow/deny remote users as required.
Snappy and reliable screen refresh
The ability to easily use features like the windows key / ctrl-esc etc etc
The feeling of a true terminal services environment (more than 1 admin at a time can work if required), but still with the ability to use the /console switch to access the actual console.