Java has this very nice utility that ships with the JDK called Java VisualVM which can provide many insights about what may be happening inside a java vm.
The steps for verifying are:
1. Have the actual java JDK installed (not only the jre) -- preferably the latest java 6.
2. Start Eclipse with -Dcom.sun.management.jmxremote vmarg (edit the eclipse.ini file and add a line -Dcom.sun.management.jmxremote after the line -vmargs -- at least for Eclipse 3.6.x -- and restart it)
3. Go on with your life until you get to something that's slow.
4. When you get up to that point, start up the Java VisualVM: it's an executable usually located at: JAVA_HOME\bin\jvisualvm.exe
5. Double click the java process running Eclipse (may appear as <Unknown Application>)
6. Go to the 'monitor' tab and check if the Heap/PermGen is too close to the max size (if it is, probably the -Xmx argument must be raised in eclipse.ini -- if you feel it shouldn't be taking up so much memory -- i.e.: there's a memory leak, click the 'heap dump', which may be a big file, zip it, upload it somewhere and point to it in a bug report).
7. If the memory seems fine, the next step is seeing up the threads running and creating a thread dump and right after it, go to the sampler, click on cpu to get sample data and add that data to a bug report (and attach both the thread dump and the sampler info to a bug report).
And hopefully, that's enough information to know what may be wrong :)