when i worked at it a little - read boardtracker every day, used a refcode whenever making a recommendation, i made around $1200 a month by referring webmasters to programs i really do like, but i never made over $2000 in a month so we're not talking the big bucks.

on the other hand, the programs with good quality recurring billing sites are the ones that we ultimately made the most with. i don't think i'd have been as successful at this if i had spammed the bigger pay per sale programs, because most people really are already signed up and also because frankly they didn't sell as well for me as the programs i recommended.