I agree with Matt's observation: if companies aren't shouting about it, it probably isn't happening.  Another option is that for those companies who are getting some success, it is likely to be localized in pockets that aren't interested in rocking the boat.

The Traction User Group conference in October had several users of that particular software talk about the impact they were having on changing the approach to using email.  Rather than email reduction being a focus of their programs, it was a happy side effect of doing more and more collaborative work within that environment (Traction) than with email flying back and forth.  The website for the TUG has a number of the presentations posted, and even a few video interviews with customers: http://traction.tractionsoftware.com/traction/permalink/Public1863.  I don't recall which ones had specific references to email reduction.  I also mentioned email reduction in my summary of the conference. http://blog.jackvinson.com/archives/2010/10/18/observable_work_at_tug2010_owork.html

Regards-

Jack