It would be awesome if the user could pass in any arbitrary data via voice commands (devs could make custom scheduler/todo list/note-taking apps that can receive data from Cortana), and even more so if voice commands could launch background tasks instead of just the entire third-party application (you could check into Foursquare without actually opening the Foursquare app and disrupting whatever you're doing).
Conversational style instead of pre-defined phrases and it just sent a tweet instead of opening the twitter app.
- He added a show to his queue in Hulu but it stayed in the app
- He said "what's up with Terry Meyerson" and it went straight to Terry's facebook profile.
And I realize that FB has some deep integration within the OS (just like Twitter)
This is a feature that would make me interested in switching to a WinPhone