There is a lot of debate about the definition of Web 3.0. there's still debate about what Web 2.0 means. Some proposals include: 3d browsing, increased bandwidth, and artificial intelligence. There seems to be consensus that Web 3.0 will include the semantic web.

The word semantic here refers to the idea that stuff on the web will have meaning whether a person looks at it or not. Instead of just a web of human-readable pages of text, imagine if the info on the web could also be easily parsed for meaningful data. The data could be both human and machine readable, with meaningful relationships easy to discern.

Microformats are one way this is already happening. The technology for using semantic web data is still in its infancy, and more standards need to be developed.

As an example, imagine a standard way of tagging medical research on the web. An application could be quickly developed to look for patterns in large amounts of research. Organizations like the CDC could use such a tool to keep ahead of emerging epidemics.