When you download TV shows in HD, you get an SD and and HD copy.
I wish that iTunes hid this from you so that you only see one copy in the library, and it automatically used the correct one.
Incidentally, I'd also like it to have this functionality with songs (the ability to have a ALAC and AAC version of the same song, but only "see" one of them in iTunes and have iTunes manage the metadata and ratings identically for the 2 copies.
Generally, a system where a "pc-quality" and "iPod-quality" version of the same media file are on the system, but made transparent by iTunes.
I really thought this was going to be a part of iTunes when I saw that HD downloads included an iPod version too :-(