While we’re on the subject of Reminders, let me remind you that they only trigger if the item is the one of Outlook’s default folders. This means if you use subfolders, reminders on items in those folders won’t work.
Not all is lost, you can use one of the two reminders utilities at http://www.slovaktech.com to trigger them.
Extended Reminders (http://www.slovaktech.com/extendedreminders.htm) works only with mailboxes and pst’s.
Reminder Manager (http://www.slovaktech.com/remindermanager.htm) works with Exchange public folders too.
[Via Outlook Daily Tips]