I like Tim O’Reilly’s definition of Web 2.0 better than the accepted definition:
Aside: I seem to have lost the battle to define Web 2.0 as “the use of the network as platform to build systems that get better the more people use them.” Perhaps it’s the lure of the obvious: companies and products that harness explicit user contribution are easier to recognize than those that pursue the more subtle and difficult task of harnessing implicit contribution. Or perhaps it’s the persistent gravitational tug of the idea that the heart of Web 2.0 is ad-supported business models; therefore, enterprise features that look like those of well-known companies featuring user contribution and ad-supported business models must by definition also be “2.0.” For me, the far more profound and powerful systems come from harnessing both explicit and implicit human contribution.
He describes Wal-Mart, Google, and the Barack Obama Presidential campaign as three examples that fall under his definition. Certainly the apps that make use of implicit contributions from users are more interesting to build.