The ones I've written have been two writers dividing up the characters. Most stories were omniscient or from the POV of the main two characters. Another one I'm working on has alternating POVs, but is written the same as the rest. Here's a line, there's a line.

Written over IM. One of us is the better editor (me) and bears the brunt of editing. However, there's something about authorial control and if a bunch of dialog needs to be edited, the other person needs the say so.

There's been some problems. I feel like I'm less likely to get suck and more likely to finish the initial writing quicker as there's someone cheerleading.

I always guess when I read. I really like to know who wrote what.