We're already offing hosted email - via VMware Zimbra that does everything that Exchange does. Management overhead is 10% of Exchange, it's far less expensive, and most important, it works with Outlook in MAPI mode. We;re also hosting our own online backup. Both of these services were easy to set up and have been rock-solid in therms of relibility. When there is a problem, I can go to the server and correct it, rather then sit on hold with someone else.