I doubt few people would be so anal to hook up to the gym's API and analyze the data to figure that out. In that sense, someone who does spend the time to do that will reap the reward for their ingenuity :)
(That said, when it comes to gyms it's pretty easy to figure out anyway. People don't tend to generally go during or immediately after mealtimes, there are fewer women during school-run times, etc.)
True, but I still think the percentage of average gym users who would go to those lengths would still be pretty small (though larger than those who'd use the API ;-)). Normal people rarely care about this level of efficiency (which I find sad, but hey).
(That said, when it comes to gyms it's pretty easy to figure out anyway. People don't tend to generally go during or immediately after mealtimes, there are fewer women during school-run times, etc.)