I'm not ready to jailbreak, but this post gave me some ideas. It would be fairly easy (given my skill-set, anyway) to automatically, whenever the K3 is connected to the PC, exchange the music on the device for a more or less random selection from the larger number of MP3 tracks that are sitting in folders on my PC. As someone mentioned, I don't want it to be purely random since the order of classical music movements should be preserved. I'll have to think about how random it should be.
I'm presuming that when you copy MP3's, by code, from the PC, they will then play on the Kindle in that order, just as when you copy them manually. But this will have to be tested unless someone already knows. How does the Kindle know what order to play the tracks? Can you access this from MS Windows?
As for answering the poll, I would say that I read with Kindle background music on about a fifth of the time.
The 44 Françoise Hardy tracks I now have on my K3 are so awesome that doing this will not be a major priority.