I finally made a web-based interface to it, implemented in JavaScript...
check it out.
Now that that's done, I can start to use friend groups elsewhere on the site. Coming soon:
1) ability to choose what groups of friends can see your posts, using the web client
2) filter your friends view to 1 or more groups.... if your friends list scrolls too fast, you'll be able to say, "only show me these three sets of friends....".
However, at this point there's no purpose in editing your groups of friends --- if you don't have the Windows client you can't actually use your friend groups yet.
Soon, soon.