A shared calendar is one of the most powerful features that Exchange provides through Outlook, where anyone in the company can coordinate meeting schedules, set appointments, and keep track of events. You access the calendar in the office, on the road from your laptop, or even in an Internet cafe or hotel computer (with OWA). It's a great way of synchronizing and updating schedules.
Hosted Exchange allows you to create and easily maintain a Global Address Book, which can contain contact information for every person in your company, as well as external contacts, contractors, vendors, etc. The Global Address Book is centralized, and always available to everyone through Outlook or Outlook Web Access. This allows you to keep contact information in one place, so it is always updated. This also makes it easier to schedule meetings through Outlook's Calendar feature.