If we were doing a blind test of unfamiliar recordings, would anyone really be able to guess whether a man or a woman was playing? Probably not.
In 1979, Harold Schonberg did an informal survey of about 270 people using a tape he made. The article is called "How Sex Plays a Role at the Piano," reprinted in Facing the Music (1981).
His conclusion: "There was an indication that there is indeed a difference between a male and female approach to a piece. Even with some inconclusive results, there were too many cases where the audiences unerringly hit on the correct sex of the performer."
However: "If any general conclusions can be drawn, it is that the more professional the listener is, the more he or she finds it impossible to determine the sex of an artist."