No company with a minimum interest in data security will ever give out their data to a diffuse cloud service - not just since NSA etc. I know dozens of mid-size companies that use Exchange and not a single one of them has any plans to move their servers or data to the cloud.
On the other hand, I can stress the complaints of other comments: Buggy initial versions, compatibility problems, reduced testing, especially of localized versions. Instead, we get 'rapid releases' that simply cost enormous admin time to install and debug. Interfaces that might look ok on tablets, but are horrible on desktops. Get real: who manages Exchange with a tablet?
Learn to listen to what your customers really want.
Not interested in Office 365, Azure, Ex2013, Win 8.1.