Great question, Mercurial Bliss.
I'm not sure gender identification affects how we present ourselves in our own posts as much as it does how we perceive the "voice" of posts by other people and how we then respond.
As far as identifing gender from posts alone, the subject being discussed will in many cases determine whether or not that will be revealed. Wonderboy illustrated this with his examples of describing sex, but if we were discussing political views, stance on discrimination, or just swapping jokes gender would not enter into it.