I was part of Collision, too, so I know what James is talking about. However, that was a round robin, rather than a collaboration. While some of issues are the same (coordination, continuity, agreement on where the story is going and what the characters will do and not do), having only two people in a collaboration does make it easier to get consensus.
I've thought of doing a collaboration a number of times, but the mechanics involved can get scary. Is it alternating chapters? Is it each person gets a scene? How much can one author suggest/make changes to the other author's work to make it all fit more seamlessly? Would it be two equals, or a senior and junior author?
While it could be done electronically, I think a collaboration would be much more effective if the two authors could sit down together from time to time to work out issues in the story.
Just my two cents (Australian) worth....