Treehouse (YC S08) has the simple sharing mechanic that Facebook needs (techcrunch.com)

I'm sure it does, what with that upcoming partnership.

Very similar to an idea I had recently for photo sharing. It's both cool and sad to see that someone's doing it.

Edit: I've done a bit more reading on this. Is this Fliggo's (YC08) second iteration? Going to their old site redirects me to Treehouse.

Looks very polished, nicely done. The real problem with new social apps (for me at least) is that I can never get my friends to join anything. Take Rdio for example, another nicely designed app -- I just can't get my friends to use it with me.