Lots of maps contain errors, including the supposedly sacred Google maps. I've seen quite a few! GPS can steer you wrong, too, although most of those are the car navigation variety ("turn left at the next intersection") that have sent people down closed Forest Service roads to their doom. I would say about that navigation "trinity," don't trust one item alone without some backup from the other! I personally don't use a GPS, but if I were going to be navigating in deep snow (I'm not), I would undoubtedly change my mind.

With maps: I haven't taken a whole map with me in years. Instead, I photocopy (on my scanner) the portion(s) of the map I need. I used to cut up the original maps, but I soon realized that copying was an easier way that would preserve the original maps. In the case of maps on waterproof paper, the copies make a far less heavy and bulky wad! I keep the copies in a gallon plastic bag so I can read the maps through the plastic and keep them dry. If they get folded to bits, no big deal, because I have the original map in pristine condition at home to copy for the next trip.

I like to use Forest Service maps (the maps of wilderness areas are particularly helpful) or similar large scale trail maps for planning. I could pore over them for hours! For the actual trip, I use USGS maps. I have the old TOPO! software for Oregon, Washington and Wyoming, but unfortunately it is not compatible with the newest Mac operating system. As long as my old computer keeps working, though, I'm fine.

I agree with Robotmoose about getting spaced out on music and missing a hazard or a turn. I've seen it happen! I don't take music with me (there's plenty in my head if I want it), but if I did I'd listen to it only when in the tent at night.