Good habit, at the very least you'll get around any permission issues with UAC.
The way i have it now is 64GB C: and 532GB D: partition on primary 640GB drive. C: houses OS and programs, D: houses data that is accessed rarely (installers, back-ups, etc).
2nd 640GB drive has 10GB P: partition for page file only and G: is 586GB for games.
3rd drive is single 931GB (1TB) E: partition for media. So if it's playing back music or video, it shouldn't interfere with OS and game activity.