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).
