Jeff, I didn't mean to make you have to rehash the standards for SURBL. I totally understood these already and I didn't mean to imply differently in my original post. (But I suppose you have to always be on your guard to prevent misunderstandings. You can never be too careful...)
But your answers regarding the corpuses were exactly what I was questioning. Basically, 1 FP in 50,000 is not bad. But if most of these FPs are "white-hat marketer" advertisements (an oxymoron?) or newsletters ...and few of them are actual human-typed correspondence, then this percentage is even better. If the opposite is true, then this might not be quite as good as it sounds.
Interestingly, I've read some phenomenal and very specific stats from Mail Filtering companies who don't get specific about these kinds of issues mentioned here and I wonder "who are they kidding".
Rob McEwen