What is Web 2.0?

This long pdf article is the most comphrensive discussion of what exactly Web 2.0 means that I've encountered (warning: written by academics). The author lists the "Six Big Ideas" driving the new web:

1. Individual production and user generated content
   
2. Harnessing the power of the crowd.
   
3. Data on an epic scale
4. Architecture of participation
5. Network effects, power laws, and the Long Tail
6. Openness

There's also a good overview of the key applications and technologies involved, as well as a discussion of what's next (Web 3.0?) A long read, and focused primarily on the effect on academia, but definitely worthwhile for those interested in web technology.