Hi there,
I carry a backup kit in my flying bag in case things go wrong which includes the GPS II Pilot I mentioned, an ICOM handheld (with VOR), torch etc. As a general rule I don't use any of these while flying but rely on the (legally required) map. Having said all that I now have a panel mount GPS which provides a handy backup as well as a full nav panel.
The GPS III will start up from cold out of my flying bag and will usually locate itself within a minute and has never taken more than two in my experience so is a good backup. I sincerely hope than I will be able to realise I'm loosing my positional awareness well enough in advance to switch it on before I get really 'unsure of position'.
I have resorted to using the ICOM and for that matter the GPS when we had a generator failure and I flew the plane for maintenance with the master off (once started of course) so they have come in useful.
I still find the GPS III a very easy unit to use - I haven't got my head around the panel mount one yet apart from simple gotos and routes. For some reason it doesn't seem so intuitive.