Okay so I got my free copy of Vista yesterday and last night while I was watching the little guy I decided to give it a whirl. Here are some early opinions:
1. Install - Much improved over XP as all the annoying input stuff is at the beginning so once that's done you can just walk away. Also install time took roughly 10 minutes compared to 15 minutes with XP.
2. Widgets - Poorly executed Mac rip-off. The look like shit and don't offer anything. That'll likely change over time as people release some cool widgets.
3. Aero Glass - very cool, Quick shut down/start up feature is also pretty cool.
4. It's a memory hog, but by comparison OSX is a much bigger hog. Regardless you can never be too rich, too then or have too much memory.
5. DX10 - If you're a gamer you already know about this. Right now DX10 is probably the only good reason to upgrade.
All in all the OS runs faster than XP did for me. Pages load quicker and things just seem "snappier" in general. I wouldn't say run out an upgrade unless you're a big time gamer looking to take advantage of what DX10 has to offer. IE7 is a joke as is the annoying pop up "warning" every time you try and install a program.
FWIW, my system score is a 5.8