Matthew A. Haughey points out some problems with buying music from the iTunes Music Store (damaged or incomplete files, and accidentally buying duplicate songs.
Another interesting problem has cropped up in the news: paying for silence. An understandable mistake considering it's not really practical for the iTunes staff to listen to each song when they rip it to an AAC file. The whole process is most likely automatic, as would be the rating system. I suspect that the iTunes gang gets two CDs: One explicit and one clean and they just pop them both into a mac (what else?) and rip away. The c|net article seemed a bit smug to me, but then they've demonstrated a somewhat anti-mac stance before.
Despite all this I'm still eagerly awaiting the iTunes Music Store to come to Canada, whenever the hell that might be.