I've been focused on e4/4.0 lately. A lot. Both on the modeled workbench infrastructure and on building the darn thing (I worship the ground Kim M walks on). But I discovered a feature in 3.6 that I find extremely useful. When importing plugins and fragments from any target platform, you now have the option to import them from (the CVS) repository.
Being able to import the source has always been useful if you want to see how something in JDT or PDE works, or if you want to tweak part of the behaviour of one of your plugins, or for the really brave, you want to see if you can fix a bug :-)
But while useful it has always been a problematic feature. Creating source bundles always lost the shape of the original project and its build information, since the source bundle is a representation of the binary bundle. The more complicated the layout or building of the original bundle, the further away the source bundle is from the actual plugin project.
And so "Import Project from Repository". Just grab the project. You have the option to take the tag that was used to build the bundle (the exact source in your target) or just grab it from HEAD (to get the latest). Fiddle with it. Reset it. Generate a patch for a fix that would actually apply to the bundle source! The committers will love you forever!!
Well, perhaps that's a little over the top, but I think it's a handy feature for plugin developers that need to poke around in someone else's bundles.