A few times I've tried to import a rather large mp3 library from my NAS into iTunes. And a few times it's got stuck. On a hunch I thought may be all the m3u files mixed in with the mp3's might be causing the problem. A quick bit of work with a smart folder and bingo, clean import.
But it took me a while to let go the Windows-isms and use "m3u" in the Spotlight bar, rather than "*.m3u", which probably means something else in Mac-speak.
