Here's a great open thread in which Mac users are discussing how they use iTunes. I'm pretty chuffed about the idea of a "Never Played" smart playlist.
I personally use dynamic playlists almost exclusively. I have the prerequisite Top 25 playlist (highest rated, random 25), the Recently Played (played in the last week) for finding something i recently heard and want to hear again, the Never Played (playcount: 0) to make sure i hear everything, and the Newest (Added after *date*), which i set up before the trip so i could listen to the newest stuff and add it to the iPod easily.
Every other playlist, with the exception of one, is a dynamic playlist with a Genre label and automatically includes anything with the specified genre. I maintain my genres fanatically and every mp3 i have fits into one of my genre playlists. The lone non-dynamic playlist i have is called Tag-Fixing and when i get new music on my machine i drag it into that playlist so i can check the tags. When i have edited the tags to my satisfaction, iTunes notices and pulls them into the appropriate Genre playlist and whatever other playlist they belong in as well. I then delete them from the Tag-Fixing playlist.
(via Kottke)