The obvious attraction to Web 2.0 is the freedom to explore, share and create that it provides. I have enjoyed the discovery of the various sites, though with so many from which to choose will admit to being overwhelmed from the get go. I loved using google docs and watching each member contribute to the team creation. I also enjoyed dancing about in Second Life, though can see that there would need to be some type of plan in mind in order to get anything productive accomplished, but maybe that is not the point. As I said the ability to share, create, and critique in a safe atmosphere is invaluable, especially to anyone involved in the arts whether writing scripts, short stories, sharing photos, videos or animations to discover what others feel about their work. It also takes some of the pressure off the teacher to be the sole judge of a students portfolio, and provides valuable feedback and ideas for improvement the instructor may have never imagined.
As with any tool, it should be part of a teachers tool box, not the only one they use. I can see where it would take a lot of effort to keep students from straying too far off the path (though as I said, discovery and exploration are important). It could also suffer from predictability or lead to mass confusion if not incorporated with interactions with other people to help guide the process. Obviously I would want to keep students from viewing inappropriate sights, sounds or words so there is an element of risk involved whenever entering the world wide web. This is also provides teachable moments as long as the teacher is aware and adept when confronted with a potentially difficult situation. I have no doubt that the use of technology to teach is here, and it is our task to use it to the best of our ability so students can take advantage of all the amazing possibilities Web 2.0 provides.