David Berlind has an excellent post on the Open Sourcing of Java. He touches on a lot of points with Open Source in general as well as the particulars of Java. The particular area that hit home with me is compatibility. He used Linux as an example. The main point there was that there really is not guaranteed compatibility between distributions. And that migrating off one distribution to another has a lot of potential issues which most customers would shy away from. So much for avoiding lock in.
I'm a fan of Open Source software. However achieving vendor independence is not a trivial task. The act of just selecting Open Source software does not provide that independence.