JS,

I don't have a G.P.S., but I've been out on mountains with people who have. In my experience, navigation with map and compass is far more accurate. One friend had his G.P.S. putting us about 150 feet higher than the peak we were on, and on the way down the map clearly showed that the G.P.S. was a quarter of a mile out in accuracy.
I have also met others people on the hills who have relied on G.P.S., and haven't carried map and compass, who have been completely lost, and have had to ask me for help with directions. Their G.P.S. also lied to them.
Add to thet the fact that G.P.S. relies on batteries, and it's a recipe for disaster in certain circumstances.
So, I don't reckon much to it. You probably won't come to too much harm trying to find the majority of sites on T.M.A., but in remote areas, especially high up, take a map and compass as well.
I'm only speaking from my first hand experience of others I've come across. I've never used G.P.S. myself.
Regards,
TE.