http://en.wikipedia.org/wiki/Female_ejaculationIn questionnaire surveys, 35–50% of women report that they have at some time experienced the gushing of fluid during orgasm.[2][3][4] Other studies find anywhere from 10–69%, depending on the definitions and methods used.[5][6] For instance Kratochvíl (1994) surveyed 200 women and found that 6% reported ejaculating, an additional 13% had some experience and about 60% reported release of fluid without actual gushing.[7] Reports on the volume of fluid expelled vary considerably[8] from amounts that would be imperceptible to a woman, to mean values of 1–5 ml,[9] although volumes as high as one pint (473 ml) have been reported.[10]
None of the women I've dated have exhibited this. But it seems to be fairly common.
It's fun to look at, and probably a fun twist in bed.