I have found that you really need to be a good writer to get these sites to pay off. If you are a good writer why not hedge your bets and also start to build your own site?
You may better try out the freelance sites like Scriptlance, freelancer etc to find online writing project and further you can directly contact the project owners for future writing works. This is one of the realisitic approach to earn.
Elance, scriptlance and freelancer are pretty good - with elance being the best in my opinion. Rentaghostwriter, wordsofworth etc are ones I’ve never heard of - but I’m going to check them out. Sounds interesting.Thanks!