IM = email?
It seems to me that the key weakness in the argument is that IM is effectively ONLY a business tool rather than a social one. For instance, technology exists to record everything that is said 'at the watercooler' so should employers do this and act upon anything that is said?
My company is heavy user of IM and it is a very useful tool for remote workers. It is especially useful to be able to record conversations (as an end user) so they can be reviewed later and important nuggets of information saved somewhere more permanent. However, just like watercooler chat, the conversations are mixed with personal comments, witticisms, complaints about the software, the clients, the vendors etc.
Employees are not generally work-robots. The few that I have met are rubbish at their jobs. Work has to be at least partly a social activity to be productive. I'm all for ensuring that employees do not harass each other, but is it really appropriate for a bunch of employees (say testers) to be griping about how buggy some software is as they go about their business of testing it?