We have a few sites that we sponsor. We tend to only sponsor sites that meet certain requirements. All my sponsored sites are high on googles ranking and get alot of traffic from audiences that would click on a hosting banner (IE not a pokemon site) I guess we have about 10 sponsored sites in total. I have found that sponsoring high traffic sites does give us more referals and traffic. Also if your link is on sites that are highly ranked in google, your own google ranking goes up. Also the few times a sponsored site got TOO big for a shared/sponsored hosting, they were more then happy to pay for an account rather then move since they liked my service