I've been using an ever larger number of Eclipse plugins in my development. I'm using Jetty Launcher, Maven, AJDT (AspectJ), Oxygen (XML editor), Subclipse (SVN support), TestNG, and a few lesser ones.
Eclipse is pretty good about backwards compatibility, so I've tried just switching my eclipse folder from 3.1 to 3.2. Should be new JARs against my existing workspace and we're off and running.
No such luck. I was working on that yesterday and I quickly got to a point where I could not convince Eclipse 3.2 to even try and compile my code. It's on the class path, I can see the class files in the package explorer, but no dice on compiling.
My sneaking suspicion is that it's the Maven 0.0.9 plugin (this plugin keeps Eclipse dynamically up to date with your project's pom.xml).
So I downgraded to Eclipse 3.1. Guess what? No dice there either.
As you might imagine, this put me in a bit of a panic. I tried deleting my project and checking it back out of the repository. Still no dice. The panic level increased again.
My final solution was drastic: delete my workspace entirely. Eclipse stores considerable meta data about your project outside the folder itself. In the shuffling up to 3.2 and back to 3.1, some amount of that has been corrupted.
It's not so bad ... it's now spring cleaning time as I'm starting from an entirely fresh Eclipse install and even re-downloading just the essential plugins that I need.