From what I have been reading about the Library 2.0 movement, it is all about information flowing at least two ways, not just from the library to the user, but from the user to the library and on to other users. All the new technologies we have been playing with and exploring for the 23 things project make this multi-directional flow of information possible to varying degrees.
The parent movement, Web 2.0 is also about that interactive flow of information becoming richer and more targeted and useful as it travels around between users using various web platforms, whether they be social networking, media sharing, or information organising applications. (See a list of 25 social networking tools here. )
With regard to libraries and the 2.0 movement, this could mean that students could in the future rate and review books held in a university library, on the library's website, so that others could benefit from peer feedback. Students could also create their own tagging of useful materials, using words that are meaningful for them rather than the traditional Library of Congress Subject Headings.
Then there is the virtual library idea, where many libraries are now making their own My Space pages or setting up real estate in Second Life to experiment with reaching people differently. I haven't explored these ideas much and will read more about them before commenting.