Funny that this was mentioned as a hot topic, because I am in the process of building 30 subscription based sites. I'll also be launching it's own private affiliate program, although I will be giving exclusive rights to up to 3 ad networks to promote the offers as well. The entire project will be going live by November 1st.
I'll be issuing a beta release to medium and large volume affiliates. The industry it's in has absolutely zero competition, and it should convert at a pretty high rate. I'll also be regulating the number of affiliates who are allowed to promote it via specific PPC engines, so to give everyone a fair shot at making the most out of their ad budgets.
The avg affiliate commission will be about $50 per signup, and affiliates will be allowed to market it with any legal means possible.
It's none of these industries either: pharma, ringtones, email/zip submits, webmaster info, adult, information products, education, entertainment, finance, etc. NONE of these big boys, just to give everyone an example..