The site approaches it in a somewhat novel way; they treat all jobs as contests, and the payment as the prize money for the contest winner.
I have a couple problems with this as a way to get work, and also from the flip side, as a way to find someone to do work. The obvious problem for freelancers is that you have to invest time into something without anything even close to a guarantee of payment. The problem for the people who have work to do is that the designs are going to be completed with as little effort as possible. Not many will spend time researching the problem and the solution when it is only for a chance at getting money.
However, an idea struck me today, and I am going to try it as an experiment. One thing about doing freelance work, at least starting out when work is more scarce than plentiful, is that it is easy to let design skills and thoughts stagnate. So I have decided that for the next couple weeks I am going to choose a contest on 99designs to spend about 30 minutes a day working on. I am going to choose a contest that has only about that amount of time left and challenge myself to come up with something great in that short of time frame.
The pressure of the short time to work on it, and the chance at getting some money from it should be invigorating and get the creative juices flowing. We’ll see what happens.