I'm all for stripping the DRM, I just did it for my kindle ebooks and am now reading them on my iriver Story. The author may rest assured that I paid him and will not copy and distribute his work over the net. It's all right.
That said, with kindle ebooks at least you can read them through Kindle reader apps available for a huge variety of devices and PCs, even keeping them all in sync. That's nice to have, but don't count on it as being the same as a personal backup.