Oh yeah quite a few times. Some women are really impressive. I like it when it happens too being a very competitive guy just beating the clock simply doesnt cut it every time...
Of course when I started swimming regularly less than 1 year ago they all lapped me constantly, even the older women. Now that I am in much better shape it still happens but really not that often. I'm also not competing, but instead just doing laps recreatively so maybe the really fast women are just not there when I swim.
This morning for instance, I had no competition
I did 2.5 km where the next may have done 1.5 km including men. The swimmers were doing something else today.