I found, well not really found, but I thought up a good idea to get traffic to your forum or site. Just go on games in Yahoo! or Google, and play a few games, and start telling people about the site or forum. I have already gotten like 30 members from just putting the url in the chat area. I dont know if it was actually 30, but prolly close.
Its just an idea. Its not really spamming, your playing the game, and chatting, so its not spamming at all, but some may think it is.
Sorry for the long reply, I'm just now reviewing this section. Yes they did register, and post a couple times. But I had to ban a couple for trying to scam people into buying stuff from them.
I think it work best for forums that are into casual gaming. Another way to get people to know about your site is talking about it with your MSN friends.