I may be in the minority here, but I've always been a fan of the Zune music software (the Zune player is a different story). The Zune software on the phone and its features in the PC client are gorgeous, user-friendly, and a refreshing alternative to iTunes. The Music+Video Hub, where the Zune player lives in WP7, now has Last.fm, Slacker, and YouTube integration, so you can easily see a list of the videos you've watched or the songs you listened to on those services. There's even a playlist creator in the Zune Player called Smart DJ (Microsoft's way too similarly named variation on iTunes' Genius Playlist) that creates mixes based on similar songs in your collection. This has been a feature of the Zune desktop software for quite some time--and it's a welcome addition to Windows Phone 7.
If you're an Xbox addict, you'll appreciate Windows Phone 7's Games Hub. The Mango update includes features previously found in the separate Xbox Live Extras app, including improved Xbox Live messaging, integrated achievements, and the ability to edit your Xbox Live profile. Oh yeah--and your 3D avatar is now fully animated. It's the little things that make gaming on Windows Phone 7 such a treat!
Enhanced Microsoft Office
One strength of the original Windows Phone 7 OS was its Microsoft Office integration. Currently in Windows Phone 7, users have access to OneNote, Microsoft's version of Evernote, which lets you jot down notes and associate images with them. Also in WP7, you can view, edit, and create documents in Word and Excel. With Mango, Windows Phone 7 owners will be able to save and share Office documents through Office 365 and Windows Live SkyDrive, assuring them of access to the latest documents when and where they want them. You'll be able to write a document on your PC, save it to SkyDrive, and open it later on your phone. This is a boon for business people who need access to their Office documents wherever they go.
In Mango, you'll be able to pin an email folder--for a project, say, or from a specific group or person--to your start screen for quick access. You can also pin an RSS feed from Outlook. Email messages are organized by conversation, so replies to a thread will be consolidated into a single view that you can follow easily. If you use Outlook for work, Windows Phone 7 makes accessing your email on the road that much easier.
Smarter and Hopefully, More Apps
One characteristic that Microsoft hopes will differentiate Windows Phone 7 from iOS and Android is its approach to apps. A new feature called App Connect will tie apps to search results in Bing.