So since Eclipse juno is based on 4.2 instead of 3.7, what is the easiest way to upgrade to it, short of installing a separate copy of juno and re-installing all my existing
Download the platform runtime binary from http://download.eclipse.org/eclipse/downloads/drops4/R-4.2-201206081400/. That is basically an "Eclipse without plugins". Run it (on a fresh workspace), select File -> Import -> Installation -> From existing Installation and point the wizard to your existing 3.7 directory. Check "Install latest versions", hit finish.
That will install the latest versions of the plugins found in your 3.7 installation into your 4.2 installation. Sadly most people don't know this feature and install each plugin manually when upgrading.
Bonus anwser: With the same wizard you can also export the list of installed features into a file that you can share with colleagues, so you have all installed the same plugins.