I'm willing to bet that Facebook has always done this with their data as well. You have to, in order to determine not just if your algorithms work, but whether they should work and what they should do.
Also, Facebook didn't 'hide it from their users' so much as 'not tell anyone they were doing it'. And for the average OkCupid user, I'm willing to bet that 99% of them have no idea this sort of thing happens. They log onto the site, do some stuff, and then leave.
Personally, I was as surprised by the idea that OkCupid outright lied about compatibility scores to see what was up as I was about the results, but it doesn't bother me, and I'm the type of person who's read all their blog posts anyway.
Also, Facebook didn't 'hide it from their users' so much as 'not tell anyone they were doing it'. And for the average OkCupid user, I'm willing to bet that 99% of them have no idea this sort of thing happens. They log onto the site, do some stuff, and then leave.
Personally, I was as surprised by the idea that OkCupid outright lied about compatibility scores to see what was up as I was about the results, but it doesn't bother me, and I'm the type of person who's read all their blog posts anyway.