I'm fairly shy both ways, but less online than off. I'll say more of what I think online. It doesn't seem to work too well for me in person; it comes out all wrong. I think I communicate better in writing; the writing part of my brain thinks more coherently than the speaking part. The delete key might have something to do with that.
I tend to keep people at arm's length, both online and off. I have a hard time making close friends, and even when I do I sometimes have a hard time keeping them, especially when they're not local. So if I seem to blow you off, don't take it personally... it's me, not you.
I can't handle being around a group of people, even people that I like, for long periods of time. I get edgy and tired and can't cope well. But I'm trying to get better about that.
I'm actually a very selfish person. I'm working on that too. Rather, I'm asking God to work on it, as I haven't done a stellar job so far.
And now for something positive... I'm usually willing to help when something needs to be done behind-the-scenes (like washing dishes after a party at a friend's house, for example).