I have certainly learned about the wonderful variety of human bodies that are out there, even if some body types and looks are disproportionately dominant on website.
On a less positive note, maybe the biggest thing I've learned is more than I wanted to know about the sex-ignorant tastes of today's thirteen year old boys, because there seems to be an awful lot of porn catering to their tastes (and couldn't possibly hold any appeal to adult men who've actually been with women). Along those lines, I've learned what a disturbing number of people have fantasies about .