Someone really needs to come up with a better term for the next generation of Internet applications and services. Hopefuly, it's not "Internet Bubble 2.0".
O'Reilly -- What Is Web 2.0
Anyway, what do I think "Web 2.0" is? I'm not sure, but I can list some distinguishing characteristics: for most of the services, the web browser is the client software. What else? Thin clients. Centralized data. Distributed applications. Open Source bias. AJAX. Mobile integration.
Next generation things I use:
Flickr, BitTorrent, Wikipedia, blogging, tagging
Edit: Also read "Web 2.0: Does it Exist, and Why on Earth Should You Care"