There seems to be a lot of discussions around what the heck web2.0 is, and if the term should be dropped.
To me, Web2.0 is as much DESIGNING for simplicity by taking advantage of enabling technological trends, as it is about the technological trends itself. Simplifying existing/legacy solutions by using technologies such as AJAX to create fundamentally improved user experiences is one of the key drivers of growth and excitement in this so-called Web2.0 environment.
Another point that should be made is of course the freedom available to users to have data mobility via open standards and frameworks. At BubbleShare, we're committed to providing user data mobility. The only true way to lock users into a system we feel is by being a world class provider of solutions that your users really care deeply about.
It obviously helps if you build meaningful relationships between you and your users, and among your users (read: community). Simply said, pragmatic and social network effects, rather than arbitrary hostage holding of user data.