I have a website which is 2 months old, and since I've created it I decided to become an active member with more than 10 forums. The very 1st that I did was to follow all of those forum guideline to make sure that my posts meet their guidelines.
The advantage of forum posting is that your links will get found and indexed by search way much quicker. Which in turn will result in higher ranking. I've been quite aggressive in doing forum posting and I plan to continue to do so. Right now my site is ranked number 6 and 7 for two very competitive keywords.
My plan is to keep doing forum posting until I reach the 1st position. Forum posting really works and I hope everyone include it in their methods of building high quality back-links.