Garmin released a new piece of software in 2005 that lets you add your own points of interest to some of their GPS navigation systems. Custom POIs can include notes, a bitmap image, and alert settings based on speed or distance.
POI loader is often used for adding the locations of red light cameras and speed traps. Combined with speed or proximity alterts, custom POIs can warn you to slow down as you approach these areas.
Here's a link to information about POI loader on Garmin's web site.