In this session, Joe Belfiore presented what he called "a big, long demo" of "early code." The session went pretty well with minor network hiccups along the way. The most important thing from a design standpoint of Windows Phone 7 Series is "nailing the UI." Belfiore stressed Microsoft's desire to make "a different kind of phone." In order to do this, the team had to "strike the right balance of constraint and hardware."
Windows Phone 7 Series is aimed at simplifying the lives of "life maximizers" (people who juggle priorities). Belfiore discussed the overall design of the device and went into many demos showcasing various hubs and functions. He spoke about the "Metro" user experience and what was done to make the OS as visually pleasing as possible. The new OS aims to remove as much of the chrome as possible, leaving maximum real estate for the things that people want to see. Motion makes the design special. It's impossible to fully experience the OS through screenshots.
There was an interesting UI element when scrolling up and down a list that wasn't present in pervious demos. When hitting the top or bottom of a list, the text/images scrunch together like an accordion, as it bounces back. The UI is not fully polished, so more changes like this one can be expected before launch. They're just the icing on the cake.
Spell correction is an interesting thing in WP7S. Instead of just correcting what you type as you go, if you still notice an error when you're finished typing, you can click the word and then select an alternative from a list. This gives more control to the user. Video of this can be seen below.
Mobile Excel was also shown off (video below). When a user opens an Excel file from an email, for example, Mobile Excel will launch and allow a user to navigate through it, as well as edit the file. You can then save the file back to your phone. Saving back to the cloud was not shown, but it can be assumed to be implemented at some point.
Music was shown to be a multitasking application. You are able to control music from the start-screen with on screen controls. The music hub also pulls information from the web to enhance the overall playback experience in both visual ways, and in functionality (video below).
It seems that true multitasking isn't really present like it is in Palm OS or Android. Yes, web pages load in the background if you start loading a page and then switch to another program. But in general, a user can't really control the multitasking experience. Mary Jo Foley found this out in an interview. The core operating system is a modern version of the CE OS and supports multitasking itself. Native code applications such as the browser and Outlook on the device will run in the background. Silverlight and XNA applications will not run in the background and when a user hits the start button it will terminate the application. Third party applications will have to use notifications to interact with the phone after they are terminated. An MSDN developer posting supports this too.