On the other hand, they are open to abuse. IP logging is nice, but only works for serious cases of abuse where a case can be made with the poster's ISP. Screening is moving too far towards censorship for my tastes[0] and involves work, and banning anon posts would be counter-productive.
Frankly, though, I don't care. If some troll posts anon without the dignity of leaving an identifying remark, fuck'em. I may take the high road and not feed them, I may say "Bollocks to it" and engage in some verbal steam-letting. Or if it's some shite which breaches the law or triggers my Retard Sense[2], I have their IP to play with.
So yeah. That's that sorted out.
[0]: I believe in the UseNet model: Talk about whatever you want. Your betters[1] will slap you around if you are ignorant or will side with you if you are intelligent, dividing people into camps (even if the only one supporting you is you). Once things are worked out in the eyes of a community, put it in a FAQ if it's not the sort of thing one wants to see again.
[1]: Yes. Betters. All the areas of the 'net that can be used for interpersonal communications are frequented by people of varying levels of ability and the successful ones have proved that the two models which work are the benevolant meritocracy and the non-benevolant meritocracy. So yes, there are people out there who are your betters and I am probably one of them. Suck it down, fucker.
[2]: Spider-sense detects danger. Retard-sense detects stupidity, of the abject, "how is this creature allowed to call itself human when there are more intelligent rocks out there" kind.