In the past, when I was searching for specific paysites, I'd usually see one lucky webmaster's code attached to the 1st/only result for that domain. Meaning that if 10000 affiliates were promoting foo.com using account #'s 0001 thru 9999, I'd usually see foo.com's link listed as
http://www.foo.com/?5498 I assumed it was because 5498 had the most incoming links or 5498 was the one the spider saw 1st or 5498 just got lucky.
I hope that makes sense & I have no idea if it still hold true (or if it ever did - lol)