A new site (new to me, thanks to Daring Fireball), Finer Things in Mac, pointed out that iTunes 9 gives you more control over your smart playlists:
Smart Playlists in iTunes 9 have become smarter. They now offer more granular, nested control over rules for collecting content.
I’ve had some pretty complex playlists in my iTunes, using multiple Smart Playlists to get to a single Really Smart Playlist; this now makes my life easier.
