I agree that it ain't a bad thing to have, just in case, but I wouldn't want to rely on it solely.

For that matter, I've thought it would be a good thing to haul images of guide book pages, first aid book pages, mountain weather forecasting info, sky charts and the like on a "reference card." A five-gram backcountry reference library, again primarily for emergencies, since "reading" a little camera display isn't always easy.

Cheers,