That should no longer be a problem thanks to Israeli hacker "Labba" who has cracked the DRM. A second hacker, "I <3 cabbages," has released the "Unswindle" program, which will reformat digital content downloaded and stored on the Kindle for PC app, converting it to easily movable formats, such as PDF.
"Cabbages" did note that Amazon's DRM process was tough to crack, although ultimately Amazon's work was in vain. "Amazon actually put a bit of effort behind the DRM obfuscation in their Kindle for PC application. And they seem to have done a reasonable job on the obfuscation. Way to go Amazon! It's good enough that I got bored unwinding it all and just got lazy with the Windows debugging APIs instead," he said.