TLDR: Yowza has paid its users about $4 apiece, on average.
Based on my napkin-math and Yowza's advertised metrics, Yowza currently has about 8000 users who have referred at least 1 person.
The top 50 referrers have referred between 12 and 500 each (about 2500 total).
So assume maybe 20k-40k registered users.
They've already given away $69,420 to the top referrer, another $6,000 to the top scorers of each of seven challenges, $5,000 to the top scorer of another challenge, and $4.20 to 10,000 users who refer at least one user. So about $159,000 paid out to under 40k users. They paid us about $4 apiece to entertain us for a day and give us an interesting art installation/piece of commentary.