Stephen Downes comments on a Joint Information Systems Committee (JISC - a UK body promoting the use of ICT in teaching, learning and research) report by Paul Anderson:
If you are new to Web 2.0, this is an excellent introduction. The author depicts Web 2.0 not simply as a new set of technologies but also as the emergence of six major ideas: individual production and user generated content, harness the power of the crowd, data on an epic scale, architecture of participation, network effects, and openness. The author gets into the details quite well - there is, for example, a nice outline of AJAX, an informed discussion of SOAP vs REST, and a good sketch of the issues between Web 2.0 and the Semantic Web.
The report can be found here [pdf]. It's quite a read, so if you need to zoom in, read Chapters 3 (Big ideas behind Web 2.0) and 5 (Implications in Education - stop at 5.4.1, unless you want to get into a lengthy discussion about archiving).