We reported a method for tagging iTunes tracks and creating on-the-fly playlists way back in January. However, it involved using Quicksilver and a couple of home-grown scripts, but we can dig it if some of y'all aren't down with a tool as broad-reaching as Quicksilver. Fortunately for the rest of you, a web designer and developer named Steven Campbell has written up a basic method for tagging iTunes tracks and creating playlists based on those tags. It more or less involves revealing the comments column in the song list for easy access, and using a simple system of comma-separated words to get your iTunes tagging on. This can work wonders for Smart Playlists, and Steven offers a few examples in his post.
For those still interested in the aforementioned Quicksilver scripts and tools, the author has issued a bit of an upgrade and a new script since we first reported them. First of all, the scripts now live at their own domain name, TuneTag.com. The scripts still allow you to tag the song you're listening to on the fly and create on-the-fly playlists from those tags, but the author also added a new script that lets you select any number of tracks in iTunes and tag them all in one fell swoop. As a Quicksilver fan I'm already in love with the power of these scripts, but either method should work well for bringing the web 2.0 tagging craze to iTunes.