That's weird, all the janitors I know have said its true that women's bathrooms are better kept than men's, and my own experience and friends anecdotes also reflects that. Perhaps there's a demographic aspect to it.
That's an interesting thought- I've primarily talked to people living in the US midwest who dealt with bathrooms used primarily by lower to middle class individuals. Perhaps more upscale locations force a higher standard?
The assumption I've always been given is that women are more prone to hovering (germs!) along with the obvious biological differences that allow for more..erm...variety in terms of mess making. Seemed a sensible enough explanation to me, but it's very possible that there's more to it.
My daughter is a student at a top-20 college in the country and shares the bathroom with 3 other girls. They are all as messy (if not more) than my son's male roommates (also in college).
Another note, I remember reading somewhere that the amount of bacteria found in bathrooms is much higher in ladies-rooms than mensrooms. May or may not be the result of overall messiness, though :-)
Interesting - I was thinking of public bathrooms, I'm not really familiar with any single-sex private bathrooms, where generally I'd assume women would have a lot more 'stuff' in general so would tend to be messier. You are probably referring to this paper[http://wc.arizona.edu/papers/90/156/07_1_m.html], which seems to be the only study ever done (and I can't find the actual paper, just people citing it). Says that women's bathrooms are tidier and smell nicer but have more germs, possibly because they touch more surfaces, they bring in children who are obviously little germ bombs, and they just use them more often (and the children angle would probably affect traffic numbers too).
