Pls Answer: What do u lose w/ migrating from Exchange to Google (gmail + calendar) for an entire enterprise?

I have a good idea what the pros and cons are for migrating an entire organization from Exchange to Gmail. However, I’d like to hear from you. Assuming the users will still be using Outlook, what pros/cons will there be around:

  1. Calendaring
  2. Mail
  3. SharePoint integration
  4. Other considerations (cost, support and maintenance, integration with other MS products)

I appreciate any feedback.