I'm looking at Eclipse 3.1M5a on my Linux box right now. I had previously fallen into using some of Java 5's convenient enhancements, like autoboxing -- Vim was perfectly happy to let me do these things. While I had Eclipse 3.0.1 calling the Ant and the Java 5 compiler, so it all compiled fine, Eclipse was pretty quick to refuse to manipulate this new-style code. I've enabled the Java 5 compliance in this new Eclipse, so I'm hopeful it'll behave nicely.
I was pleased to see that it picked up my old workspace nicely, and once I reinstalled Subclipse, the version control and decorations were still in place. I was fearful that I'd have to spend another couple days trying to get my project setup properly.