Well I've just started with eclipse (2 days ago), and already I LOVE it! But from what I can determine so far, it seems the problem would be that it doesn't yet have the advanced features of other IDEs. For example, debugging web apps and things like that. However, I really like their
philosophy - i.e. providing a development platform that accomodates plugins rather than trying to lock you in to a product suite that's expensive, and after you get locked in, if the product suite doesn't have what you want you're out of luck.