Tweeting is not writing. It does seem like a conversation, however; one-sided, of course, but conversational.
This from Anne Lamott's Twitter feed:

"Here is how I'll write: not beatifically, not with great self-esteem, not with any real sense of what I'm doing. But I'll do it because I get to."

I love writing. Writing is the only thing that takes my mind off all the other shit (like people obsessing about us instead of seeking psychiatric treatment for their own inability to be happy) and when I write, I feel free.
It's like swimming. I don't bump into walls and coffee tables and buildings when I swim. In the water, I am graceful and fluid and strong.I don't sink like a stone because I suck at small talk, I don't drown because I'm socially awkward. When I write, I am a fish in water. Where I belong.