Web 2.0, a quick refresher. These notes are in progress. Of course.
Web 2.0 marks a shift from the Web model where we focus on single documents and their accumulation into sites. Instead we dwell in: microcontent, services, and moving with pieces across multiple sites.
Some concepts usually attached to Web 2.0: stigmergy. The web as a place for building stuff. Sharing content, and socialization stemming from that. Open source, or something close to it, like open content, shareable APIs, RSS, and open standards.
The usual examples and suspects: blogs, wikis, Flickr, del.icio.us, 43things, YASNs, podcasting, vlogging, RSS. Open APIs and projects therefrom, like Google Maps' (check out this Flash version).
I'd add a few other Web 2.0 suspects and sources to this now standard mix: mobile devices making and using microcontent (cell phones, PDAs, iPods, still cameras, video recorders, DVD players, etc). Alternate reality games, which only exists insofar as their content is broken up, shoved around, and discussed across a bunch of fora. Discussion boards, to the degree that content pieces are addressable (can I link to your post?) and open to external services (can I blog your post?). Dynamic Web design, to some extent, and Web pages drawing on multiple content pieces, like linking to someone else's banner, sucking down updated content into a frame, ad services (although see below).
About that Web 1.0/2.0 break: it would be good for someone to write about Web 2.0 antecedents. As noted above, some Web 1.0-ish page design actually uses 2.0 approaches, like microcontent drawn in from other sources, services to push updated items, and so on.