If you are playing around with the Linux version of Flex Builder, CFEclipse, or generally mucking about with your Eclipse, or need to upgrade to a new Eclipse version, you've no doubt been annoyed at the way this removes all your carefully installed plug-ins.
Fortunately there is a way to keep them across Eclipse re-installs.

All you need to do is create a few magic directories and one file:

# mkdir -p ~/eclipse-plugins/eclipse/features
# mkdir -p ~/eclipse-plugins/eclipse/plugins
# cat ~/eclipse-plugins/eclipse/.eclipseextension
name=My Eclipse Plugins
id=my.eclipse.plugins
version=1.0.0
#

Then in Eclipse itself, go to Help, Updates, Manage.
Right click the top of the tree, and choose Add, Extension location.
Pick the directory you created above.
Eclipse will want to restart so your should probably let it.

The next time you install a new plug-in, make sure on the final install screen you change the 'installation directory'.

The next time you have to blow away Eclipse, you can just re-add the extension location to get all the plug-ins installed into it back, hurrah !