The fragility of e-readers does worry me, too, especially if your libary is primarily just stored on the e-reader.

Just the other day, my mobile phone got drenched inside the pocket of my rubber rain jacket, even with the pocket flap snapped closed. I never imagined water could get in there, but the wind was howling while I was waiting for the bus and I guess that was enough force to push rain under the flap and into the pocket. I've been trying to dry my phone out for a week but it looks like it's done for. There must be dozens of "totally unexpected" ways that your e-reader could be knocked out of service in a survival situation.

Also, I assume (I don't have one--yet) that these e-readers use some sort of lithium ion rechargeable battery? Regardless of how well you treat them, lithium ion cells do degrade. So, for a gadget that you might just keep in storage for years, waiting for a chance to use it, you may find that the battery will not hold a decent charge when you need it.

So, I think an e-reader is a great tool, but it's a rather vulnerable single point of failure that could take down your whole library at once. Certain critical items such as important maps, first aid and edible food reference books, etc. should have some redundancy, preferably in a non-electronic form.