If you are in the process of understanding the Microsoft Online Services offering BPOS(email, shared calendars, online meetings, messaging, document management etc...), this is a good starting point. Microsoft has recently published a whitepaper that discusses the business value of online services and a cost analysis for hosting your services on-premise or "in the clouds".
Below is an excerpt from that recent Microsoft Whitepaper.

"When you add Microsoft Online Services to your IT investment mix, you gain potential added value for your business in four main areas:

• Finance: Reduced capital and operating expenses.
• Process: Enterprise-class availability and highly secure operations.
• Technology: Faster deployment of new services with access anywhere for your staff.
• People: Simplified and more secure user and administrator access to services so that your staff can focus on the core business."

To read the full article go to http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=9061e5e6-ea23-45c0-8389-0dfd63674356#tm