Part of my experiments with money making was to try to diversify the advertisers I used.
So I put Adbrite on this blog and also on another niche blog, and left it there for three months.
My conclusion: Adbrite is rubbish. The ads served up are so inappropriate, no-one would ever click on them. eg they were putting hideous weight loss picture ads on this blog which is about making money. So I've removed them.
For now this blog will be ad free till I think of what to try next!