The term Web 2.0 describes a resurgence in the web economy and a new level of interactivity between the internet and the viewer.
The main idea of Web 2.0 is to make website more simplistic. The images and words that are selected for the website should be simple and concise enough to make sense. The images need to be more about communicating the message of the site and not just to decorate it. You should think of pixels as a resource that you have a limited supply of. You don't want to use too many pixels when you could do it with less.
Web 2.0 should be "simple, bold, and honest". This is why lots of web 2.0 sites are center. It feels more honest.
The book, Save the Pixel, looks like it could be a good read about designing for Web 2.0. It has 20 full web redesign case studies. It helps a designer learn to simplify web pages.
A web site about Save the Pixel. It goes more into depth than the savethepixel.org.