There's a brilliant slide illustrating what happens when people use email to work on documents together on the Wikinomics blog (which I found via Euan Semple's blog).

It's great because it illustrates how this way of working creates multiple instances of every document which makes the identification of the record that bit more difficult. It also shows how complex the information flows become when a group of people are emailing various copies of the same document to each other. A comparison is made with using a wiki for the same process. There's more than one way of working collaboratively so I'm not sure that the argument that a wiki is the best way to do this is completely over, but the slide certainly makes a compelling point.