Efficiency of StumbleUpon advertising ?
zealog: While I have never done any advertising on StumbleUpon, I will say that my experience with traffic referred from SU matches with many of the other comments here. They will generate a lot of hits but quality is low. The bounce rate is many times higher than other traffic sources and the return rate of those visitors is almost non-existant.* As a disclaimer, I do know someone who has an upper level job there, but it's pretty clear that hasn't influenced my opinions about the service. :)