I was back on the air this morning and decided, on a whim, to set myself an esoteric theme challenge and have all my non-playlist tracks be from artists starting with the letter R. Completely invisible to anyone listening and probably not even apparent to those reading the playlist online. But since I hadn't planned ahead it kept me on my toes looking in the Rs of various genre sections. It actually made the show more interesting and I think I'll try it again in two weeks with a different letter.