Would feel lost without my little garmin pilot III. (Not literally!)
It appears to be extremely accurate when flying, but in my experience, useful as a toy only when driving. Even less useful when walking. Despite re-setting the datums to, I found innacuracies of about half a mile, when I used mine for walking in Cornwall last year. Not much use if lost in fog near a cliff top.
As a side point, I was out walking in the Peak District last week, noticed this old geezer, fiddling with his little hand held. Looked absolutely Pi**ed off, wife looked even more bored. It was a beautiful day, you could see for miles from the tops---couldn't help thinking that he was missing the point somehow !