Should Web 2.0 trust user data?

CrashRoX writes: "One of the big hypes with Web 2.0 is that users should be able to control their content. We then end up with assortments of mashups, widgets, feeds and customized pages/profiles. My question is where do we draw the line on what users can do? MySpace is the best example for this question. They got there start by promoting the fact that you can have a page that displays your personality, customize it and pretty much do whatever you want to it. Over time they had security problems with users using JavaScript. That privilege was revoked not to long after. Most recently they limited some flash control and started banning certain widgets (youtube and others). Sites like Google let you create your own widgets using an API. My question is how much control from a programming, security and usability point of view should we give users? What guidelines should developers follow for building web 2.0 sites?"