This is an interesting example of exponential growth:
I had the apple banner running at adhitz for a test. With one dollar per day, I was averaging one referral per day. Not bad.
Today I upgraded my budget to make it $2 per day. I get home and...BOOM!...notifcations for 5 referrals!
It is only one day but another encouraging thing was that the time of the notifications were one every hour. So it only took 5 hours to run through my clicks to get these. If that is the case then there is room to grow
The cost per referral drops from 90 cents to 30 cents each (if you factor in the 10 cent signup bonus they pay) plus I should win the referral contest which is another 2.50 for the week