I like to keep Outlook open all the time, but I don't like to have it on the taskbar all the time.
To minimize it to the system tray, start regedit and follow the steps below:
HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 10.0 \ Outlook \ Preferences
Data Type: REG_DWORD
Value Name: MinToTray
Data: 1 (0 to disable MinToTray)