Hello,
All points made very valid - at least take some spare AAs and as the Garmin manual itself reiterates, do not be wholly reliant on one source of navigation.
Nothing yet made is goof proof. I lost valuable water reserves - tears of laughter - when a very serious type lectured on the use of a sextant for desert navigation. 'No battery or circuits to bugger in these' he proclaimed loudly. Then dropped the rather delicate instrument off the roof of the Landy he was stood on - bouncing off the roof rack, bonnet, camp dog etc on way down!
I got a Garmin GPS12 about 6 years ago - was doing a lot of stalking in a Forest Enterprise block in Dumfries - the ground was very hard to follow and the unit saved hours of getting 'unlost'.
It was a worthwhile purchase even employed as back up/ double check to map and common sense. Reception in trees is iffy however - they do need a good patch of clear sky.
Just acquired a Garmin Extrex Summit - exact same principle, but lot more user friendly and lots of features. It is best to KISS on many occassions and the etrex unit seems to be layered - ie you can use it simply or delve deeper as you choose/ feel more confident.
The Summit - and possibly other units - has a location sunset/ sunrise read out which can be useful for stalking. It also has a barometer giving crude weather outlook data and more importantly tells you how many feet you've climbed - strangely always seems to read about a third of the height your legs/ lungs tell you!
With the US turning off SA, I found both units quite accurate. Just nipped outside and checked GPS grid reference against the OS map - using the scale on the edge of my Silva to accurately break up the grid squares. For a Morayshire Sunday evening my unit was accurate to within about 2/3 metres.
Know your basics, never lose the practise of fundamental woodsense/ map/ compass navigation; but by all means get a GPS and enjoy it.
Hope that helps.