You have heard of the Digg effect right? This is what a successful thread in the Google forum can do to your Alexa rankings: http://www.alexa.com/data/details/traffic_details?url=www.biz-dir.co.uk Not to mention the 17 submissions ($750) I got over the weekend or the natural links I accumulated, usually I am lucky if I get 3 or 4 on a weekend.
DP can send clients your way! I know that in a blue moon someone contacts me from an old thread I posted for my services. So of course if your thread is popular it'll give you more exposure so more clients