We trialed SimpleCDN in some simple cases for files I've had on it, and the performance was pretty bad as measured by Pingdom across the world. I love the idea and wanted them to be good, but it simply couldn't perform for us and always seemed to be serving from some place in the central U.S.

Maybe they've gotten better in the past few months, but they didn't do much for us except for give us a reliable alternative hosting location. The performance never seemed to improve worldwide-- almost as if they don't have many edge servers.