Joshua Porter has written an “Introduction to Web 2.0″ pretty recently—seems to be quite a comprehensive overview of this topic containing links to major resources, basic examples and so on.
Apart from that, he also wrote posted some bits about folksonomies today—quote:
“…But now we know why folksonomies are valuable. It is because they do two things very well.
- One is that they allow people to remember things in the way that works for them. Someone tagging pictures in Flickr or bookmarks in Del.icio.us can use tags that they’ll remember. Instead of working twice to shoehorn a resource into and out of a taxonomy, folksonomies let users do both tasks effortlessly. Reduced cognitive load. Don’t Make Me Think. (if you didn’t read Rashmi’s A Cognitive Analysis of Tagging, you should).
- The second thing is that they easily enable a bottoms-up classification system. When folks tag multiple resources at the same time, it is easy to aggregate those tags and provide navigation and resources that expose them. This is the reason why popular resources by tags on del.icio.us (like Web 2.0) and Flickr Interestingness are consistently valuable.
It must be stressed, however, that over the last year that we’ve learned (nudged along by Vander Wal) that the first is much more important than the second. If something isn’t valuable personally, it will rarely be valuable for the community…”
Interesting stuff (imho). 
