I used 99designs to get a book cover designed and I was very happy with the results. My designer was responsive, friendly, and made a wonderful design that went above and beyond what I was expecting.

However, I was unhappy with how little the designer actually received. I paid $799 to run the competition, and the winning designer only got $387! Charging >50% commission seems highly exploitative, especially when all the designers who don't get selected receive nothing at all despite spending spending time creating designs.