Nowadays, there's not much difference, but a few years ago, we were practically opposites, to the point that I actually saw myself as having dual personalities.
I've always preferred the way I acted online as opposed to offline, so I tend to try to behave like my online self in real life - I am my own role model.
The only real difference is that online, I have more time to think, and it's easy to look things up so that I have enough knowledge to discuss whatever subject happens to pop up Therefore, I tend to say quite a lot more online about subjects I do not really know much about, and my language tends to be more eloquent and correct when writing. However, this is not really a major difference in personality, simply in circumstances.