It's not an ideal solution, I know, but it is completely painless -- it even copies the MP3 tag info from the AAC files to the MP3s. I wrote this to finally get my large collection of iTunes-purchased songs onto my Sansa -- start it up at bedtime, and by morning, you're all set wtih MP3s to drop right on the player.
You can read more about the script, and download it, on the Hijack Recorder page on my site.
[robg adds: I haven't tested the script, but I like the idea of having yet another way to back up my iTunes store purchases (yes, I've already burned them all to CDs).]

