How Facebook killed spam

1. Applications unwittingly installed by naive friends that post annoying updates all the time to my wall, effectively hiding the little signal in there. Each time a friend uses a new application I get more spam until I hide it. A variant of this is the unhideable notification that a friend started using a new application; getting rid of these requires hiding the friend forever. Both these examples require an action not simpler than using gmail's "filter messages like this" function to mark them as trash.

2. I have some relatively popular friends who are often unwillingly tagged in cheap promotions, religious events (they're atheist), musical events they're not attending, etc. This effectively spams all their friends with a "this person has been tagged" notification until they decide to remove themselves from the list.

3. I have also received unsolicited facebook messages of a very dubious comercial purpose that I would report as spam in gmail.

All in all the signal-to-noise ratio in facebook ends up being so low I have a twitter account specifically for keeping up with friends, and it ironically enough makes it easier to do the low-cost maintaining people usually associate with facebook.

Most of this comes from the fact that, while I mostly trust my friends, I can't trust all of them (as refusing friend requests is usually seen as very rude), and while I can (and do) hide friends, I can do nothing about the bad friends of my good friends, and those end up being a regular source of spam.