As a dogfooder who tried Windows the Vista Beta, man has this product come a long way. Kudos to the Windows team for dramatically improving just about everything in the product.
Here's some key things to remember:
Backup your files - Always good advice, but don't forget to export your IE Favorites and your OPML blog roll from your favorite blog reader before starting.
My PC: Dell XPS M170 (pre dual-core), 2GB RAM, 80 GB Hard drive.
My Installation List
Other Personal Notes
All-in-all, I think users will be pleasantly surprised by Vista and the sky is not actually falling.