How many drafts of a novel do I do? I have no idea.
My revision process doesn’t quite work in a linear complete draft kind of way. Most of the time, I revise scenes as I go along. Some novels like Luck for Hire and Fuel Eaters were written fairly straight through in a very rough beginning-to-end manner. Divine Fire, which I’m currently going back to, didn’t have an ending for a long while. But there’s never really any "second" draft. Just a continuous reworking of the original with new layers added and subtracted.
A bigger problem, especially between collaborators, is the matter of revision control. I get pretty uptight when Eric is working on the same manuscript I am, even if he has opened a new document for the part that he’s rewriting. Ideally, I’d like a "don’t touch it until I’m done with it" philosophy, but that’s not realistic if we want to get anything done in a timely manner. Generally, it works pretty well when documents are labeled with the date and initials and put into a common folder in the computer network.