Like I said about how quick it can remove something complicated like those videodrivers; it's pretty much coded from the ground up to be faster and more efficient and more stable in what it does
7 can also run anything that XP can, even switching itself to virtualized XP mode if it has to.
Windows 7 never froze or crashed on me ONCE, and I have been using and abusing it for 2 months now.
It takes advantage of modern hardware (my favorite part of vista), while remaining rock solid in stability; native Blu-Ray burning and scalability for my extra RAM and triple videocards for instance
Big UI chages; one thing is that the UI is built for easy multi tasking with options to manipulate open windows to perfectly fit your screen space, I use this feature a lot now.
Those might not be extremely compelling reasons to upgrade, especially to yourself who prefers an OS to be nothing more than a clean slate to install your programs, but they are really good improvements and as justifiable an upgrade from '98 to XP ever was