A little over a year ago, I gave a lightning talk at the W3C Technical Plenary in Boston where I looked forward to what came after Web-2.0. The key insight underlying that talk was that the Web was now mature enough for us to build Web technologies purely out of Web parts. Web-2.0 is a result of applying the Web to itself and is therefore better thought of as Web(Web()) or more concisely, Web2.
Today, we can build new web artifacts out of existing ones by aggregation (web mashups) and by projection (filtered views), and publish the resulting artifacts on the web by assigning them a URL. This leads to the insight that this web that is to come potentially consists of the power-set of all web content. These ideas, and their logical consequences are detailed in article entitled Toward 2^W --- Beyond Web 2.0 in the February edition of the Communications Of The ACM. You can also find a slightly more extensive blog I posted here.
