I too have been very disappointed in the Nav system. We first used it on the way home from the PCD and thankfully we knew the way home. It would tell you turn when there was none anywhere,make U-turns, and send you in the complete opposite direction when there was no way whatsoever to get home.
I have tried it numerous times and it sends you the longest and with most traffic each time. Only 2 or 3 times has it gotten me out of a lost situation.