Much the same as the OP for myself. Calibre to strip DRM and keep all copies in one location on my PC that is backed up nightly to 3 other hard drives, and also (but not as frequently) to a netbook, a server and Drop Box. I absolutely would never trust the stores where I purchased books to keep them available.
I only keep up to 500 books at a time on my readers, which gives me plenty of choices to read, and just swap more on when I delete some. Those 500 are also on a micro SD card in my wallet just in case my reader locks up while out for a day so I could still read in case of a reset.
I'm pretty well protected against any disaster whether I'm away or at home.
