The only times I usually role-play is during Halloween time, when the other forums I go to (YouChew) allows users to change their profile to reflect a character, then post on the forums as that character. The exchanges that go on during this time are often hilarious.
The forums tried to implement a subforum dedicated to roleplaying, but it fell through because no one took it seriously. What a shame, since it had so much promise. All it takes is a few spammers to completely ruin a good idea (like what happened to that site's chat feature).