So I've been using Eclipse 3.3 for a while and was anxious to get new features and better performance out of it. So I started using Ganymede (3.4). I held my breath until M5 and then I caved in and installed it. Then M6, then M7, and now RC2. What I can say is that M5 was good, but then I had issues with M6 and M7. Finally, RC2 is improved in terms of stability.
Still, it simply freezes from time to time.
It still does not take advantage of the dual core's out there, but I guess this is actually Java's fault, not Eclipse's.
Too bad that some of the plugins I've been using before are not working on Ganymede. For instance Weblogic Server Tools plugin which stopped working since M5. Well, time will fix it :).
I applaud the efforts to provide pre-packaged versions of the Ganymede download as it really was a pain to jump from one project to another in order to assemble a proper J2EE development environment.