Google Apps is a service from Google for using several Google products with custom domain names. It features several Web applications with similar functionality to traditional office suites, including:

• Gmail
• Google Calendar: allows for a shared calendaring system, allows for easy embedding of calendars on websites and sends out automatedmeeting invites & tracks RSVPs
• GTalk: a chat system for easy and swift communication
• GDocs: a shared documents space
• Sites: tools for easy creation of sites for business

This allows for a flexible, sound and easy to understand intranet system providing a powerful messaging platform (email, IM, calender). Click here to read more detail.

As well as a collaborative platform (Document-sharing, Google Sites). Click here to read more detail

Why the Premier Edition?

• 25 GB / account Vs only 7 GB/ account
• Email and phone support available
• Additional email archiving and email security services
• Secure internal video sharing
• And so much more… (Please refer to http://www.google.com/apps/intl/en/business/editions.html for more details)

Aids in adapting to Google Apps

• KiGoo, an application running over Kayxo Insight technology
• Enables users to manage Google Calendar through the Microsoft Outlook interface
• Allows for managing of email and Google Contacts from Microsoft Outlook
• Allows for offline browsing of information
• http://www.getkigoo.com/
• gSyncit, Allows synchronization of Gmail & Outlook contacts (including photos and groups) and calendars

Will there be system failures/ downtime?

• Google Apps Service Level Agreement guarantees that Google Apps Covered Services web interface will be operational and available to Customer at least 99.9% of the time. If this is not fulfilled, Google Apps offers service credits or service extensions to customers.

  Source: http://www.google.com/apps/intl/en/terms/sla.html

Here’s more information from independent reports around the cost of Google-Apps (hosted service) vs an on-premise solution.