LifeHacker has a pointer to this curious service: Criagsnumber.com. I suppose the goal is to allow you to post a phone number in your Craiglist classified without posting your number. Though, Craigsnumber.com isn't actually part of Craigs List.
It's a neat idea and is free, so it seems like it would be really useful.
Now the only person you're sharing your number with is craigsnumber.com, and the question is, do you trust them?
Of course I do, but then again, I trust just about anyone.