You can see that DaniWeb has the social icons here. It allows you to facebook share or tweet about the current forum thread. Facebook friends and twitter followers of the person who clicked the icon then see a recommendation from the person about the page, and it helps spread good content among online friends and people with similar interests.
ohh god yes add the buttons ASAP the knock on effect for increase in traffic can be in some cases quite good.
i.e if i click on like on your site it publishes that to my facebook meanwhile my 500 friends on facebook (most of them bored and snooping on peoples pages) a % of them could click on that like and be brought to your site increasing traffic.