If you are trying to set up an appointment with another individual, you can quickly send an e-mail that will show your calendar availability/schedule. This can make it much easier to coordinate an appointment with others.
You can change the time increments shown in your Outlook calendar to allow for smaller more detailed calendar entries. This will work in Outlook 2003, Outlook 2007, and Outlook 2010.
Creating a shortcut to open an email pre-addressed to your email address will allow you to quickly take notes or create a reminder to yourself. This will work with Outlook 2003, Outlook 2007, and Outlook 2010.