I came from an Incredible.
Pros:
-Battery life is way better
-Faster (better FPS in games, faster rendering in web browser, loading apps, etc.)
-Better call quality and reception
-Larger screen!
-Much better build quality (metal vs. plastic)
-Better camera quality (stills and video)
-With 2.2 and LauncherPro, home screen scrolling smoother than the Incredible
-8GB of internal storage can be used for apps
-I can see the screen easily outside, even in direct sunlight
-802.11n wifi
-3 microphones for excellent audio recording
-Gorilla Glass
Cons:
-Sense UI is better than Motoblur
-I miss the Sense UI widgets
-On my X, the speaker is adequately loud, but the Incredible's is a little louder
-Camera app loads slower and the interface is less intuitive; also, there is no tap-to-focus--you'll need a third-party camera app for that
-I like the Inc's black status bar over the X's white, but I suppose that can be changed by rooting the phone
-Overall, out of the box, the X is inferior to the Inc in software quality. But there is a whole Android market out there!
-Must remove battery to access microSD card