Summary of features covered
1. Simplicity
2. Central layout
3. Fewer columns
4. Separate top section
5. Solid areas of screen real-estate
6. Simple nav
7. Bold logos
8. Bigger text
9. Bold text introductions
10. Strong colours
11. Rich surfaces
12. Gradients
13. Reflections
14. Cute icons
15. Star flashes
http://www.webdesignfromscratch.com/web-2.0-design-style-guide.cfm
I like web20 websites but I think you must add this option in the list. Web 2.0 sites must be user friendly interface.
We must ready for Css 3:)