Have you listed to the Yaminade podcasts yet? They really are great and very informative. Inspired by Naomi Moneypenney’s podcast where amongst many other things she talked about how her organisation doesn’t use internal email. Which is incredible but makes sense on so many different levels.Her company uses Yammer internally instead of email.
You can also read her great post: “15 Reasons Posting a Yammer Message Might Be Better than Sending an Email” here. She also has this video on her page as well which I had to include.