With my "must try all the things" geek hat on, when I saw a thing called RetroShare mentioned, I had to download it and give it a try. Or more accurately, when I read the wikipedia page for retroshare, I had to download it and give it a try.
So far, it looks good. If it delivers everything the wiki page says it does, then I like it. As far as I can tell though, there are even fewer people using it than there are using Diaspora*, and that isn't exactly flush with users at the moment. (NB - that may just be that I haven't managed to find the right circle of people to get in with, I recall the early days of twitter were similar, and I struggled to get up to following twenty or thirty people, and I now follow, erm, well over seven hundred.)
Apparently this link should allow you to add me as a friend on there, but I'm guessing that depends on if your browser knows what to do with a retroshare:// link or not. If not, here's my public key
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.4.9 (Darwin)
-----END PGP PUBLIC KEY BLOCK-----
Apparently you add this, then send me your public key, then we're connected and can chat/message/share files/various other things in a full on decentralised way. I'm not sure how it copes with machines that are not on full time - I assume that when you're using it on a laptop/home desktop that is rarely on, it is somewhat like ships passing in the night.
Now if only I could find someone else who is using it to test that assumption.