Ever since I heard about how well they work, I've always tested ugly ads with hand drawn elements in them. For some some strange reason, they seem to get better CTRs. If you are a regular user of Prosper202, you may have seen some of my handiwork when you login to your account.
For example take a look at this masterpiece
This Ugly Ad has averaged a CTR of 1.09% after almost 11,000 impressions
This fancy looking banner below didn't do so well
This More Professional Ad has averaged a CTR of 0.06% after 9,000 impressions. We quickly took it out of rotation.