P.S. If you want your iPod to live-update that playlist (using a "last played is not in the last x days" rule), you'll need to sync all the smaller playlists to your iPod as well as the main playlist, so the iPod knows where to pull tracks from. If you don't want the smaller playlists taking up room on the playlist menu, you can throw them in a folder. I put all mine in a folder called "XYZ" so it appears at the bottom of the screen, out of the way.
But if you don't care about live updating, then you can just sync the main playlist and be fine.
Daily use: 3G nano 8GB, 4G touch 8GB
Previously used: 1G nano 4GB, 2G nano 4GB, 2G touch 8GB