some time ago we were a publisher partner for Valueclick. The returns were very poor so we dropped them.
Never used them for PPC advertising. We did use Google, but found them to be hopeless, very expensive with a very low conversion ratio between clicks we paid for and sales made, making me wonder if people were just clicking the ad and then immediately exiting the site.
I have just left a question for S123's support people asking why I cannot see our ads when I use their own search box (from the public home page, not from within the account). I see only Teoma listings there, not even any competitor's ads. I regard that as absurd.
We have had a small account with S123 since April and have had zero conversions.
I have had moderate success with them. There seem to be some bogus clicks, but a fair amount of legitimate traffic that converts a bit below Google or Overture. Overall, perhaps a 50% conversion rate compared to G or Ov, but decent. If they cleaned up their traffic quality a bit, they would be very good. In my experience, they are significantly ahead of Enhance or Kanoodle. Kind of like a 75% Findwhat.