I also use one main install, and symlinks for most of the guts and copy it 4 times. a while back i found an awesome app that someone posted about here, it puts the symlink stuff in the right click context menu, it really makes it easy to do symlinks and all that jazz, its called Link Shell Extension, it works with every OS i've had and it saves a ton of time, a bit off topic i know, but i thought id throw it out there.