First of all, I doubt that there is a REAL me. There's a series of personalities which I put on, depending on my moods; and a series of traits and interests that I have. But, I don't know that there's too much fundamentally underneath this. If there is some soul or whatnot, it is a tortured and erratic thing, flying through both pain and ecstasy, but usually numb these days.
As to any sort of dishonesty in real life, I'm the same arrogant fool everywhere. I never know what can and can't be said. Nonetheless, I'm never so immoral as to intrude on those who don't already know me IRL, though I've learned to do so more on forums. But, that's not really too different either, as the forums are rather like public meetings, and I have never had too much trouble getting up in front of a faceless horde and telling them what I think.
Actually, when I think of it, when I'm in a small group of people, I either clam up completely, or am essentially playing the crowd. Maybe my one on one relations are exactly the same way - I don't know for sure. I certainly put on different personas when with someone. Even when alone. I think that this is really what everyone does though.