I've been watching the Web 2.0 meme for a number of years. I run an online community site that could be said to fit into the Web 2.0 realm. At first, the term Web 2.0 stuck me as a clever bit of ironic marketing: traditional software comes in nicely packaged releases, therefore wouldn't it be fun to pretend the next 'version' of the www has just been released. Well, the marketing worked and the term has gradually come to represent some of the newer and more interesting trends in website construction and use.
The IMIA has recently set up working group to look at how Web 2.0 is affecting healthcare. There is a portal site at: http://differance-engine.net/imia20/and a new Ning social network: http://imia20.ning.com/
The Medical Librarian's Association also have a Web 2.0 group and have recently released the results of their into Web 2.0 usage amoungst librarians: http://sns.mlanet.org/blog/2007/09/24/what-mla-members-told-us-about-social-networking/
There's also a recent 'Blog Carnival' to celebrate Web 2.0 in Health Informatics going on: http://healthinformatics20.blogspot.com/
If you want to keep up-to-date with Web 2.0 in Healthcare, Bertalan Meskó's Scienceroll is the blog to watch.