We also think reminders are great for, well, reminding! We can make sure everyone knows what time to arrive, what to bring (or not), your address, and all the important details. If you forgot something on your invite, like your phone number or to ask about food allergies, this gives you an opportunity to do so.
Reminders definitely don't have to be fancy. Just a quick and friendly e-mail to the guest list works just fine for us. Many invitation websites like Evite will often do this for you automatically.
How do you handle reminders?