The other half bought a Garmin Dakota, one of the early ones, about 4 years ago. It's awesome, we haven't looked back since.
We spent a week biking in the Lakes using just this piece of kit. Downloading routes of the internet and riding other peoples trails. Niether of us had any experience of riding in the Lakes so being able to go out and ride at a decent pace all day without getting the map out at every junction was an absolute god send. I don't even recall getting significantly lost.
Theyre also nice on a road bike, opens up the lanscape a bit as you can never ride off your map! You can adopt a "well lets see whats down there" attitude without worrying about it, instead of doing your rehearsed loop all the time.
If you're a technophobe it may not be so easy. You need to use alternaticve software to plan your route and then export this to the unit. It's too small and fiddly to plot a route on the unit itself, certainly on a Garmin.
The other option is to use someone elses route off a navigation/GPS site. This can then mean converting formats to get the one your specific unit requires. Again a bit fiddly and you end up flicking between sites to convert files on the web.
However the rewards are def worth it and I now have a wealth of rides on my pc I can call on at anytime, and also the understanding to use anyones route, anywhere in the UK! Thats a lot of riding and has to be the future of MTB.
Also being able to used AA batteries is an adavantage, especially if you dont have a OS map to back yourself up (not reccomended) Please use this approach with care if you are out somewhere remote!!
Happy trails 
