For any document of non-trivial length and more than 2 people, use some kind of shared access:
Source control (subversion, cvs, etc.)
Single shared-storage Office documents with change tracking
Google docs
etc.
Agree on minutae early: naming, style, point-of-view, voice, etc. Enforce these decisions, and explicitly make new decisions as soon as possible when new ambiguities arise.
Don't let an individual or part of the team go off and write part of the doc in isolation for an extended period of time.
Unless your writers have worked with each other for a while, the text you get back won't fit with the flow and style of other sections
There may have been a miscommunication as to the nature of the section
There is a tendency to put off completion of the section to near the deadline for the whole document, making editing or a rewrite impossible
For large groups, someone needs to be a technical executive have final say in decisions of scope and content. This is often not the same as the manager.
As your team grows, stronger leadership is required to limit meeting length, frivolous discussion, and the effects of standing disagreements.
more tbd