Outlaw Design Blog has an article on How to Review your Portfolio through Social Media Design sites.
Concept Feedback is a nice site that practically guarantees you will receive feedback on your design within a day or two of posting. It’s a great place to hear what other creatives think about your work.
Uses Twitter as a tool to get reviews for your site or design. Seems ok, but reviews are limited to 145 characters.
This website cost money, but is pretty affordable. It is more based on usability, but seeing as how usability and good design go hand and hand, it seems like the site could be worthwhile.