I noticed that when editing shared maps, the password is shown. This leads me to believe that the password is not stored in a secured fashion. Password should not be able to be decrypted, let alone shown on a webpage. This makes me question other passwords that Garmin stores.
If you use a common passwords people (you should not), I suggest you change all Garmin passwords until someone responds. As you may be aware, there has been many major website compromised releasing username/passwords in recent times.