Microsoft Outlook Launch Stats
techcrunch.com
techcrunch.com
So what Gmail users are really switching to is a less complex webmail service in Outlook. I believe Outlook is trying to disrupt the webmail industry once again, but they are using a less complex model to do so. While Gmail has become more and more complex (not necessarily a negative), Outlook seems to be going back to simplicity.
I suspect the mix is almost entirely Hotmail upgrades. It is very hard to get people to switch even if Outlook was much better than the alternatives.