We did try guest posts once.





Shit loads of spam.





Turned them off.

Of course, if they can be coupled with a CAPTCHA and a daily post-limit by IP, they may work better.

Edit:

I've just been going over a few threads in the Staff forum to find the ones about guest posting. We decided in the beginning that CAPTCHAs and limits by IPs were a pain, because people wouldn't be able to quick sign-up and post - they'd have to wait for all the confirmation e-mails. After a while, which just so happened to see a huge number of spam posts, it was decided that guest posting was to be stopped, as the vast majority of posts were spam, and we had a tiny ratio of people registering (something like 200:1).