Would be interesting to see what the survey yields. Some possible indicators to size this:

1. Total revenue passengers in 2012 - 17.3 million (up from 14.7 million in 2011). Making some very simplistic (and likely stupid) assumption that 5-10% of "new" passengers enroll into the program and a higher percentage (possible 15-20%) of the "old" ones enroll - I'd venture a guess that the number is between 2 and 3 million

2. Lufthansa has 20+ million members in its program (should be more; this was announced in 2011) while it flies nearly 90 million passenger every year. Assuming same "propensity to enroll into the FFP" for Lufthansa and Jet, Jet Privilege members should be closer to 3.8 million. But if I had to guess, I'd think awareness/attractiveness for the Jet frequent flyer program is lower (awareness leading to lower new enrollments and attractiveness leading to more people banking miles on other preferred airlines) - the ratio of passengers flown to FFP members should be lower for Jet, again bring it down towards the 3 mil number (rather than 4).

Going through the annual report, there is another interesting thing that one could calculate - How much is the value of a Jet mile to Jet itself? (using data from Passenger kilometers flown and provisions for frequent flyer miles made annually). It's likely to be lower than how much we do (0.23 to 1.08 from other thread on value of a mile) - that should be another survey we should do