I've investigated it but never used it. I know a lot of people who do though. It can be more than just jobs for writing articles, and can include things like website work, graphic design and much more. It works on a bidding system, where people post the jobs and you bid on how much you will do it for.
A lot of the clients out there looking for workers do go cheap, but will often end up with cheap results. People learn that going with the cheapest bidders isn't always the best idea, and many people will pay to get quality results.
I know people that have had both good and bad experiences with it, but I think that goes with every one of these type of services.