The above post is incorrect on the specifics.
Points2Shop/Cashle pays out $0.50 on Sign Up if the referral confirms their email address.
A bonus $0.50 is given when your referral completes their first offer (only one offer) that pays 2 points or more.
Members not from US/UKA/CA (yes Canada is the same as the above as well) then you still get bonuses but it is pennies and your offer completion percentage drops from 15% to 2-3%.
But either way, it really depends on how much effort you are willing to put into it. I've seen members with $7,000 + from referrals in under a year.
As for my personal method it would be to create a website promoting the idea and use SEO to rank for specific keywords.. it's really the same as most other types of promotion.