P.S. re: all this talk of line endings (and thank you eschwartz for the amusing overview), I feel like a child sitting at the grown-up's table struggling to understand what you're all talking about!
I edited the text files using an HTML editor on Mac OS X, then saved the file in "plain text" format, and it worked nicely on my Kindle.
I'm curious: Did it work because I saved it as plain text (i.e., does plain text = *nix line endings?) or did it work because I'm on a Mac and OS X is Unix-based?