I drove about 300,000 miles for work in the last five years with no GPS. Bought one this Spring (Garmin NUVI 755T) and once I started using it, it became indespensible. I installed a power supply on the bike and made a bracket for it as well. I hear instructions/music via headphones. I use it daily in the car, but only on 1 hr or longer trips with the bike (or new areas).
It's not foolproof, that's for sure, but nicer than Mapquest printouts, etc.
