The Windows Phone Blog has a nice writeup on the new features we will see in the Mango Music + Video Hub. We've known about some of the features for awhile now (see our "Big Mango consumer list" for what we know so far), but it's great to have official confirmation and more details. There are also quite a few smaller updates that don't merit their own bullet point, but will help smooth out the experience.
The on-device podcast support is a welcome feature, and many users have been asking for it since day one. The iPhone supports it out of the box, and there are a few apps in the Marketplace (e.g. Bring Cast and Podcasts!) that offer some podcast functionality, but so far, only Windows Phone has announced on-device podcast subscriptions, baked into the OS. The standard download-for-later, and stream-it-now options are supported, and users will be able to download or stream over WiFi or GSM/CDMA. New podcasts will only download automatically while your phone is charging, though, and for now, it looks like this is a US only feature.
One of the Zune's greatest features is the Smart DJ (see earlier leak). Smart DJ mixes have always been playable on your Windows Phone, but you've had to create them on your computer, and transfer them over. Mango will give us the ability to generate them on the device, by just long-tapping the "seed" artist, song, or album, and selecting "smart dj." The Music +Video hub will then store your mixes in the History pivot.
To round out the experience, the team has modified the UI/UX a bit. They have moved around a few items, like the repeat and shuffle buttons, to make them easier to find, added bigger playback control buttons, added lock-screen music controls, better images, lockscreen album art, a streaming icon, and on-device playlist creation.
Jump on past the break for the full changelog from Microsoft themselves...it's quite the read.