Hmm, hard to say. One thing that isn't reflected online that is a big part of me in person is probably how much I
don't talk. And when I do talk in person, I would say it's generally less detailed and more awkward. Discombobulated speech, with words often completely out of order.
I haven't been a member of this forum for too long, but how I am here differs from in person is that I am more serious, logical, and to the point here. In person around people I'm comfortable with I'm extremely sarcastic and light. And technical and annoying :

: In the past on forums I've joked a lot, reached out to people and showed interest in their lives, and genuinely cared about the people I met and interacted with, as well as was very open about myself and my life. Most of the time in person I am the opposite. Very avoidant and trying to keep to myself and not letting anyone in. I don't know though, I think to a degree after a while the person I was online and the person I was offline started to converge and now there isn't so much discrepancy anymore.
Seeing me in a chatroom may be more accurate than a forum though, since life isn't like Ok, here's the topic. Now sit down, think it over, and respond in a articulate and detailed manner that you reviewed." Of course I'm still the same person, even if the different mediums bring out different aspects of my personality.