A List Apart has an interesting overview of CSS3 animation and user experience .
I have seen a few of these effects around, and they really add to the user experience while being pretty light.
Featured Software Print your Folders quickly
Print and visualize your folders. Find out where your hard drive space went – and all your hard to find junk files.
Save money by avoiding buying a new hard drive, when all you had to do was delete files you didn't even know you still had!