Yeah, World Winner and King are your two largest skill gaming websites. I have played on both for quite some time. I made a good $1000 a week playing pool. I then quit at the beginning of 2011 because they decided to raise rakes. Anyway, you can still make money, just have to practice..
I don't think its worth it if you do it legitimately but if you have a bot doing it for you then go for it or if you have a bunch of people who are willing to sell you runescape gold below the market value you could sell it and get a profit