In regards to the mainsite, I think it's mostly habbit that keeps brining me back there. Checking up on it is part of my daily routine, and it has been for the past couple of years. Although with my new account I am going to make an effort to post art on it and look for art relevent to my interests on it. I could always do with a bit more art in my life.
As for the forums, while I only signed up today I did lurk here for a bit mostly just to cure boredem.