We first heard about iTunes Tagging back in September
and it looks like it is going to make an appearance at Macworld 2008. iTunes Tagging, in case you don't recall, is the name of a method by which one would dock their iPod with an HD Radio. You hit a button when you hear a song you like and that song's info is 'tagged' onto your iPod. When you sync your iPod with iTunes those tagged songs show up as a playlist which lets you easily purchase the songs.
that since many HD Radio broadcasters and manufacturers have signed on with this technology Apple is ready to push it onto eager consumers. It sounds interesting, though I can't recall the last time I actually listened to a radio (HD or not).