For those who have 550's; Just got back from a 4300 mile ride, Zumo locked up three times. Would not respond to anything. The solution is to unscrew the battery, count to ten and replace. It all comes back to normal. Also discovered that some of the route calculations involve some trully idiotic combinations - I guess the programing guys in Mumbai are not as swift as advertised! Also, don't blindly follow instructions ! this thing will repeatedly send you on secondary dirt roads and even off a clif if you are not carefull! Fording streams on dirt roads ain't my bag on a 900 pounder ! Yess, it did happen.