With 99designs we found the original, distinctive and evocative logo we wanted for the small amount of money we had as bootstrapping startuppers.
We received 163 designs from 15 designers in 7 days.
In the past we used individual designers in a traditional way and I am absolutely sure that it would have never been possible to get such results that way.
We found some feature particularly useful (e.g. making the contest private, inviting designers, guaranteeing award) and some interesting ones we might use in the future (e.g. reaching the designers offline, 1-to-1 invoicing).
Special mention goes to 99designs customer service (namely Justin), who intervened timely and brought some valuable and unbiased suggestion and real help.