I really love my GPS (Magellan Maestro 3100) system that I received last Christmas as a present from my mother. I use it whenever navigating to new places I have never been before and it is always pretty darn accurate.
So it worked as usual without a hitch, calculating the best route flawlessly, on my way to Angel Sword last Saturday. On the way back, however, it sent me back on a different route which ended up making the 50 minutes trip take 10-20 minutes longer due to sticking me on backwater highway roads with only 1 lane, and getting stuck behind old geezers going below the speed limit. This had made me really mad at the time, and rather confused as to why it chose a different "fastest" route back; that is until I got to my destination and found out there was heavy construction on the highway going northbound (my way back) that had delayed one of my friends for 4 hours on his trip into Austin :-O. Glad I ended up following its directions after all and not going with my gut and taking the same route I took down there!
My fatal mistake was assuming the GPS calculated the routes itself instead of asking a central server elsewhere with traffic information. Now I know better!