I have had a couple of "friendships" with people who only knew me online. They knew my name because I had done business with them first. We were enthusiasts about the same types of books or whatever. But I had already changed my name, so they had no reason to suppose that I wasn't male. It was liberating to be seen that way, but I worried that I would out myself or that they would find out somehow that I was legally female.
On forums where I used an alias, I felt much more comfortable being myself, even to the point of not worrying that I might out myself. Oddly enough, I never did let the cat out of the bag; and as far as I can tell, a lot of people
assumed that I was male. I was even labeled sexist (in a bad, evil male way) and chauvinistic on a number of occasions, when I voiced my opinions about abortion or children or sexual relationships. I felt much more comfortable airing these opinions anonymously because people did assume I was male. When I said such things in person, people were often disturbed by my...unfemale attitudes. When I said them online, no problem. I was just labeled a guy--because, you know, a woman could never possibly hold those opinions.

But all of this was pretty conscious on my part. Well, very conscious. Deliberate.