The term "Web 2.0" is commonly associated with web applications that facilitate interactive information sharing, interoperability, user-centered design, and collaboration on the World Wide Web. ( http://en.wikipedia.org/wiki/Web_2.0
The emphasis on interactive and information sharing is the most interesting to me.
Reading a book is usually a singular activity. Then you join a class or a book club and you get to discuss why the characters did something or what the author was trying to convey. Now you have more insight into the characters than you had before, whether you agree with the other people in the discussion or not.
The same is true for setting up an agenda, creating a presentation or espousing an idea that is new to you. If you work in a vacuum, you may not see some possibilities that would improve your output. The ability to create and receive feedback from a variety of points of view broadens your understanding.
Another aspect that fascinates me is the user-centered design. Everyone learns things differently. The interactivity allows an individual to replay or redo something until it becomes part of his/her knowledge base. There is no one around to criticize the amount of time it takes to learn the particular subject.