I\'m using Eclipse 3.6 with latest Sun Java 6 on Linux (64 bit) with a larger number of large projects. In some special circumstances (SVN updates for example) Eclipse needs
You can go to the Preferences -> General and check the Show heap status. This activate a nice view of your heap in the corner of Eclipse. Something like this:
If you click the trash bin, it will try to run garbage collection and return the memory.