I've done four or five campaigns with blogads.
With good graphics and sharp text, I could get my clickthrough rate up to about 00.13%, like a semi-barely-decent content or facebook. The trouble is that most blog owners overvalue their own traffic, charging way too much, so you can't really make money with that sort of CTR and those rates. The conversions also seemed somewhat weak when compared to regular google content traffic, or facebook. (There are some exceptions if you look.)
Having said that, however, I will say that some of the best money I ever spent was $2000 I invested in a blogads campaign to launch a new gossip blog. All of the gossip blogs I bought advertising on (except one) gave my blog permanent blogroll links, and frequent in-post links (lasting to this day, two years later), and a lot of the traffic I bought through the ads has stuck around for the long haul. That gossip blog of mine has turned out to be a steady money maker with almost no effort on my part (thank to bloggers who are willing to work dirt cheap). So there ya go, thumbs up to blogads for that.
Anyway, someone must be making dough on blogads (t-shirt makers perhaps?) as the same ads always running on certain sites. Do your homework and you can probably figure it out.