Very slow Eclipse 4.2, how to make it more responsive?

It looks like Eclipse in silence have created a fix and announced it in all secracy through their wiki (!). It seems to alleviate the problems for me at least; though I have not tested it in length yet.

See http://wiki.eclipse.org/Platform_UI/Juno_Performance_Investigation

Basically you should install the "Juno SR1 Patches/Eclipse UI Juno SR1 Optimization" from their 4.2 update site: http://download.eclipse.org/eclipse/updates/4.2

Bug-tracking for this optimization: https://bugs.eclipse.org/bugs/show_bug.cgi?id=394588

There are known performance issues with PDT 3.1 and eclipse 4.2 (juno).

https://bugs.eclipse.org/bugs/show_bug.cgi?id=385272

This is the solution:

Open a different perspective (for example java, but not php) and restart eclipse. Afterwards you can savely switch back to php perspective. Eclipse will have no performance issues.

Also mentioned here

Actually in looking at your machine configuration, you should make sure nothing else is going on in the machine and experiment with reducing your required memory, say something like -Xmx512m. If you are requesting too much heap space, then it's possible you are doing a lot of OS paging.