I don't try to hide the fact that I'm female, but I don't use it to try and get attention, either.
People online tend to respect me, take me seriously, and are friendly because I don't post slutty pictures and constantly talk about my sex life, e-flirt, and make every post about "OMG I HAVE BEWBS."
Anyone who needs to use the fact that they have breasts to get attention over the interwebs needs to stop and reevaluate their priorities (and possibly their mental health).
Offline I'm a professional, hard-working, personable, intelligent person and that's what I like to convey over the internet, too. I get annoyed when people get the wrong impression just because of my gender.
And then there are those folks who think I can't even have an opinion about certain things...
Well, that's my rant