Forum posting is great for getting backlinks. I usually join many forums and post away with a link in the signature. I know people don't like doing this these days, but sometimes we have to start somewhere right?
I agree that forum posting is a very useful way of getting some traffic, but bare in mind that it's not the best way, and it's simply a lot harder than one would think. The best way to gain traffic from a forum, well, that's to actually post a lot on a single forum at a time. Gain around 1000 posts and see if traffic flows, if not, move to the next site. You'll still have those backlinks on that site.
I agree completely with you Steven. It would require a lot of posting on a forum to get anywhere, but it would require thousands of posts on many forums to get by.
I agree that the only way to generate traffic is to post a lot. And it usually comes down to posting often though. So the more you post the more traffic your site will get.