I thought I read the 500 can do "courses" but not "routes" (which the 205 and 305 can do).
If I'm right the 500 can show a "course" and you can follow it, and I guess it beeps when you go "off course". What I thought it couldn't do, which the 205 and 305 can, is to follow a user generated "route". By route I mean a series of linked waypoints which when you use to navigate it gives a beep each time you are approaching a waypoint and flips to a screen which shows the direction of the next point.
Basically from what I read the 500 seemed a downgrade from the 305 (and even the 205 if you are not interested in heart-rate or cadence monitoring).