I've also had problems with the GPS turning itself off, either due to rattling or old batteries of duff rechargeables. I don't always notice either, especially if I'm going over familiar roads where I don't need the GPS for direction.
Saying that, it would certainly make it easier to ride DIYs along nicer routes. There are times when I've had to miss out on certain roads/routes purely because of a lack of an appropriate control on one section. Being able to rely on the GPX for proof of passage for some subsections (not even all of the ride) would be very useful.
It would also make convoluted routes much easier. For example, I'd like to be able to do the Surrey Hills route as a detour from home to work (or vice versa) as a DIY 100. It's possible to DIY it, but it means compromising the route.
http://www.bikely.com/maps/bike-path/167493The problem is the lack of anything useful in Ewhurst. There's a pub but I'd be looking to do this early in the morning when it won't be open. I can DIY it by moving the control to Cranleigh but that pulls me off the route that I want to take.
Being able to use normal controls (Putney, Epsom, Dorking, Epsom, Putney or Waterloo) with the GPX file for Ewhurst would solve this problem.