It seems to me that many, maybe even a majority, of corporate employees who use Microsoft Outlook and Microsoft Office really don't need a large amount of the functionality provided by the large corporate expenditures needed for the required software licenses.
I bet many such employees could do their jobs just as effectively using Gmail and Google Apps hosted by Google through a Google corporate account. The huge concern for many corporations, of course, is having their information hosted on Google servers.
Even that concern might be overstated when you consider how many employees fall victim to phishing scams that result in corporate network security being compromised, regardless of what email application they use.
I think any corporation paying for licenses for Microsoft Exchange and Microsoft Office for each and every employee should take a hard look at the bottom line and consider whether alternative strategies might serve them better.
Why more businesses are going Google Apps | ZDNet