My understanding of the attraction/repulsion forces I feel with Twitter seems different, but they might very well be the same thing at bottom.
On the attraction side: There are circles of people online that I want to feel "in" with. I also like the "hit" of suddenly getting lots of positive feedback from something I have said or written online. If I'm honest, I might just like these feelings purely for their own sake; they may have little or nothing to do with the actual people involved.
What repulses me is the gap between the acceptance I want and the acceptance I actually get. Also the gap between my non-knowledge of a topic or set of references and the educated way in which the cool, connected people discuss them. Finally, the unlikelihood of my ever being able to affect either of these things in ways that will actually improve my standing.