Good stuff here: http://blog.uwinnipeg.ca/schwagbag/archives/2005/03/im.html
So here are some of the pros and cons (for our particular situation), and my general questions . . .
Pros
it’s saves several thousands of dollars a year ? it’s free!
it works ? bonus!
no messy setup or clunky interfaces; uses a medium that many/most students are already familiar with
ability to create customized ‘queues’ per subject or librarian for things like subject pages (simply create an appropriate and different screen name for that purpose), which with VR software can cost around $3000 per librarian
it’s ‘disposable’: one thing that really bothers me about our current system is that all questions and transcripts are kept for three months, and in terms of privacy issues, we have no control over that
Cons
much more challenging to keep statistics
lose the ability to refer and track email questions (a component of our VR software) among numerous subject librarians
I think the stats issue could be handled without too much muss and fuss for most libraries. A database could be set up on the IM computer and each questions could be entered and cataegorized: reference, informational, etc. Then you’d have some good stats to pull out.