Bad news for me. Rockbox isn't supported on iPod Classics so I'm stuck with bilious iTunes and its single genre restrictions (amongst other things)! And it's got me thinking that I wouldn't mind working on the Rockbox project but I don't think I have enough hardware knowledge (my degree is software oriented).
Btw, I've been using your script today Tore and it seems to work pretty well. The only modification I've made is adding .replace('&','%26') so that it can handle artists/albums with ampersands.
And so far, the genre categorisation at discogs.com seems to be reasonable except for when it comes to metal. They don't consider it a top-level genre so that means that every metal band gets tagged with Rock whether it's Burzum, Wormphlegm or Stratovarius. Occasionally ambiguity causes amusing genre tagging such as Death - Human being industrial/power electronics and Freak Kitchen being house.
Now to wait ~20 hours for another 5000 hits (not to sound like a crack addict).