I like the idea (as much as I like any advertising) - so it's like putting someone elses page ads on your page, the referer's in your case. So imagine they had Adsense on you'd want to display the same category of ads on your page too (or possibly ads for the same companies?).

Not come across this at all. Which referer's are you expecting to clone the ad categories from specifically? I say this because most referers on my blog, say, are Google (!) and so the keywords of the post generate ads (Adsense, Amazon) that are relevant as if they were on the Google search page (the referer).