I'm running Eclipse SDK 3.4.0 on Mac OS X 10.5.6.
Every time I try to install something new through "software updates", the message "The software items you selected may not be valid with your current installation" shows up.
So I'm going to uninstall it and re-install Eclipse.
Should I just erase the Eclipse folder or is there a way to uninstall it?
I just had a similar problem, with the GWT-PlugIn not showing up in the interface. Deleting the eclipse folder did not solve it, GWT was still there! Deleting workspace didn't work! But deleting the .eclipse folder in the home directory did! I'm working under WIndows 7 here, but it should be the same with OSX. But you may have to make the folder visible first. Under linux based system, folders starting with a dot are invisible by default.
This folder was probably the reason I had problems in the first place. If I remember right, I switched from basic Eclipse to EE, but didn't delete this folder.
In my opinion, an uninstall skript would do Eclipse quite good.