GPS - Like any other flight instrument
I have 3 learnings about GPS, which may or may not be on thread. Firstly, I always use SirfStar III Chipset in GPS for PDA's, Car Sat Nav or the hand held GPS I use for flying (Garmin 96Cx) this isn't a specific flying GPS, but I use it in conjunction with Memory Map and I like it. (I have tried memory map on a PDA etc and I didn't get on with it!) The handheld GPS is more rhobust than PDA's, simpler and it takes 2 AA batteries, which is easy to change on failure.
So the SirfStar III Chipset seems to be a lot more sensitive than other chipsets and as such maintains the signal and locks faster than other units I have seen. It is now the only thing I will use. I have never lost the signal when flying or driving with it (except through tunnels and I don't fly through those very often!)
I have a degree in computing, so I never read instructions. I pottered out on a 'local flight' to test it. I had the unit in Course Deviation Indicator. I now know that this will point a relative bearing along the line between two points and the VOR like break in the middle indicates how far off course you are. I became disoriented because I was expecting it to point at the next waypoint, but it wasn't I thought I really new where I was, but I was getting information I did not understand and I did not like it. Now I was tracking the M1, so nothing was really lost, but I about turned and got back to the VRP Pronto and was pleased to see it. I will tell you a valuable lesson was learnt there. This kit is complicated, you need to understand how it works, make sure it is programmed correctly (and be ready for a mistake!) and you need to be practised in it's use. Just like any other piece of flying kit. I now use it as part of my navigation tool set, along with may watch, compass, DI, VOR, DME, NDB, on board GPS, etc. etc. etc. When I jump in my car with my Tomtom, I don't give it a second thought - but it is definitely different in the air! I practiced with it in the car, parks etc. etc.
I wish they spent as much time teaching about GPS including handhelds as they do about the VOR, during PPL.