This is a discussion on Recreational Players vs. Grinders? within the online poker forums, in the Learning Poker section; If you would have to guess, how many recreational players versus how many grinders would you estimate are playing on Pokerstars at various stakes?
At the micro stakes you won't find many grinders, maybe 1-5 % I'm guessing, and those are most likely just trying something out. At the high stakes, for example at 5000 NL, I would say 95-99% grinders. At 50 NL and 100 NL, I estimate it to be about 50-50.