Can you tell...

[Nimcha]

I find it really hard not to associate someone's gender with that of their avatar, even though it's usually totally wrong. It also depends on where I am. On a gaming site like this i assume almost everyone is a guy, but if I'm on, say, a fan site or fanfiction site I assume almost everyone is a girl. So no, I cannot tell. But I don't alter the way I act, because it happens to me, and it's not a big deal. I know most people think I'm a guy when they read my posts, so the whole gender on the Internet thing becomes pretty normal after a while.

Same here really. I usually try to guess from their avatar or username. I have a shoddy hypothesis that states most female users have usernames with either an A at the start or the end of the name.

<--- case in point!

 

[ajofflight]

Generally no, although the rare times that I venture a guess, I'm right, more often than not [sub]knocks on wood.[/sub]

 

[Floppertje]

I can tell when it's a long conversation in a chatroom or something. usually not from forum posts.
and my attitude doesn't really change that much, except i'm a bit more careful with crude jokes.

 

[DkLnBr]

the username might give it away, and (if the case may be) the avatar. other than that, i cant