The Outlook 2007 feature Quick Click is a really nice feature; a Quick Click is a defined action to be done when you are single clicking a column on a mail item. You can define Quick Clicks in the mail item views for the columns Categories and Flag Status. Right click the column and select Set Quick Click… to change the action.
For example; you can define the Quick Click in the Flag column to add a flag with a Tomorrow reminder (default is today).