As promised (and as a sign that Microsoft isn't forgetting about Zune HD to work on Windows Phone 7), the Zune 4.5 update brings more video codec support and Smart DJ music discovery to the player.
I checked out Smart DJ on the Zune, and it's really similar to the Genius playlist on Apple devices, except if you have a Zune Pass (their $US15 unlimited music subscription) the Smart DJ will download music directly from their store onto your player. This makes music discovery quite easy and convenient, since all you need is Wi-Fi access and Zune HD will gobble down 30 songs (some of which are from your own library) that are recommended for you. Quite neat, and meshes well with Zune's focus on music discovery in addition to just enjoying your own stuff.
Other cool things: Picks, which are recommendations from the Zune service (culled from community preferences as well), and the ability to browse and stream music from the Zune Marketplace when the Zune HD is docked to your TV. This makes it a nice Pandora-esque music-from-the-cloud setting you can get just by docking your Zune. There's also MPEG-4 Part 2 Advanced Simple Profile, which includes Xvid and AVI container support.
The download is going to be available in a couple weeks, and even Microsoft isn't quite sure when it will hit. We'll let you know when it does, cause Smart DJ is actually quite good when combined with a Zune Pass (which we like by itself already).