I outsource work on eLance, and this made me investigate. For anyone else wondering, eLance's terms state that any IP for a project belongs to the employer after payment is made:
This is definitely something that is important to be aware of and to have clarity on. Future investors and company buyers want proof you own the IP in your business if you're trying to sell it.
You should also check similar agreements on 99Designs, Freelancer.com, oDesk too to be sure you actually own what you buy.