Hmm...Well, I have two general attitudes in real life. When I'm with people I don't know, I tend to use much more refined language, attempt to show that I have a respectable IQ and try and be as polite as possible (barring unusual circumstances where politeness would be inappropriate or uncomfrotable). When I'm with friends, I tend to be significantly more laid back (and, curiously, significantly less wity. I don't consider myself to be a particularly fast thinker, but I always seem to do better in that regard when I'm not with friends and family).
The internet doesn't change that very much, save that the vast majority of those I interact with are strangers. As such, the more formal aspects of my personality come to the fore. If I'm comfortable with someone I know on the internet, that will generally soften a bit. That said, since I tend to stutter and such when I get excited and speak too fast (this happens frequently), speaking intelligently is substantially easier online (without even bringing into the equation the fact that I can stop and think about what I'm saying/typing).