Outlook Users (Also useful for switching from Thunderbird!)
Here are some tips for making the switch from Microsoft Outlook® to Google Apps. 
Switching from Microsoft Outlook®
Life After Microsoft Outlook®

Quickly learn to accomplish some of the same tasks in Google Mail that you're used to doing in Outlook.

Print this guide out and keep it handy as you begin using Google Mail.

Many of the same features from Outlook are found in MHC's former email standard, Thunderbird. While the specifics between Outlook and Thunderbird are different, the answer to the question, "How do I do _____ in Google Mail?" is generally the same.
What's not available in Google Mail  See features you might be used to in Outlook mail  that aren't in Google Mail.
Switching form Microsoft Outlook®: Gmail and Calendar

Self-paced training (short clips - 1 hour total) A comprehensive introduction to switching from Microsoft Outlook® to Google Apps. Covers threaded email conversations, contacts, labels, mail filters, calendar events, syncing events from Outlook, and more.