I have never seen co-editing effectively used.
The recent launch of Microsoft's Office 365 generated many comparisons between it and Google Apps. See "Office 365: First Impressions" for more details.
Many of these comparisons note differences between the co-editing features of the two products. Co-editing is a feature where multiple people can simultaneously make changes to one document.
I have never seen co-editing used effectively!
Here's a quote from a promo video for Google Apps expounding the virtues of co-editing: "it's almost like we were sitting side by side". But I ask you, when was the last time you tried to share half of your keyboard with a colleague?
The idea is that by simultaneously working on the same document together (co-editing) you get to your end goal faster or create a final product of higher quality. The experiences I have seen point to the exact opposite outcome.
Remember the old fashioned days of collaboration with flip charts and markers or more recently whiteboards? How many times did these sessions have multiple people scribbling away at the same time? In fact, at many sessions, "passing the marker" and having a rule where only the person holding the marker talks was a necessary and effective mechanism to manage the flow of ideas.
I have found that scheduling a "collaboration" session to co-edit a document usually provides participants with an excuse to do no preparation and often no one bothers to read any background information until the session begins.
Starting with a blank document and trying to develop content through co-editing is downright painful, the amount of pain increasing as more people are added to the co-editing session.
Sure, a collaborative review of a document through desktop sharing can be effective, but I have not seen the effectiveness of this type of session increase by allowing multiple people to change the document simultaneously. Having one person control changes at a time, perhaps rarely passing control between participants, seems to get the job done--and in every case I have seen with less confusion and in less time.
Whether you are sitting in the same room or collaborating via cyberspace, technology cannot make up for bad work or communication habits. Sometimes too many cooks can spoil the broth, or at least significantly delay the meal.
At no time in the production of this document were two or more people simultaneously modifying its content.