Yet another cautionary tale.
Preceding Amazon Kindle's now publicised capacity to arbitrarily delete content without notice or permission
is this other blog post about the joys of digitally restricted (read: deliberately broken) content -
Kindle’s DRM Rears Its Ugly Head… And It IS Ugly
Essentially, with Kindles you are only allowed an unspecified number of downloads to an unspecified number of devices; you are not entitled to know how many; new devices may void your download rights altogether, and if your downloads start failing thats too bad you need to buy your content all over again because you never really owned it anyway. And if you complain, you're probably a liar and a thief.
Significant inroads have been made against rights managed content, but the war is nowhere near over. So, unless you actually have no problem paying money for vapour that could vanish in the blink of an eye, avoid feeding the DRM beast and stick to hard copies, or soft ones that have no restrictions and allow you to back up. Take note you I-retards.