Though support for the feature was added to iTunes 7.4, iTunes Tagging remains one of the least-understood expansions of the iPod ecosystem—arguably, for good reason. Developed by Apple and implemented in new iPod speaker systems by companies such as Polk Audio and JBL, iTunes Tagging enables an HD Radio tuner to record information about the currently playing track, save it to an iPod, and let the iPod’s user easily find that track in…