With car routing, it will often have me zig-zagging through a residential area to cut off the angle when it really would have been faster just to stay on the main road, go down to the corner and turn right. It will sometimes take you down busy shopping districts with lots of red lights, when a truck routing would miss all that. Sometimes it will have you exit the Interstate and continue on the frontage road for a couple of miles and then get right back on the Interstate. One time on I-65 just north of Mobile, AL it had me get off, drive around the block and then get right back on. As I was heading back up the on ramp it giggled a little.
You do have to pay attention. Sometimes I'll run the route on the Garmin and then run it on Google Maps on the phone. Sometimes the Garmin can't find an address, so I'll look it up on Google, find it on the map, and then select that point on the Garmin and have it route me to it. Sometimes I'll fire up Streets & Trips and/or PC Miler and check the routings there against Google and the Garmin. Streets & Trips is good for "big picture" planning and for quickly choosing alternate routes and checking mileage, which can either confirm the Garmin is correct, or you can translate the S&T routing to the Garmin manually via waypoints. It's all a matter of what works best for you. But you will eventually get burned one way or the other regardless of what routing method you use, whether it is one the above mentioned methods, a trucker's atlas, directions from a local, or following your own instincts.
