Affiliates and referrals do have the potential to bring in a good income on a monthly or quarterly basis. Most of it would be through webhosting sign-ups.
A significant number of hosting companies run one referral or affiliate program for sure. If you have a blog or directory which attracts a lot of such relevant traffic, then more often than not, you would generate some income through affiliations. However, the amount of money you would get would depend on relevant traffic you get and the payouts.
As always, beware of those who say they will payout thousands or millions for one sale, it never is true