Microsoft has posted the Windows Phone 7 Jump Start Sessions, which consist of 12 videos (each of them is about one hour).
The Topics are:
Session 1 - Introduction
Session 2 - Building a Silverlight Application, Part 1
Session 3 - Building a Silverlight Application, Part 2
Session 4 - Building Games for the Windows Phone 7 Platform
Session 5 - Building XNA Games for the Windows Phone 7 Platform, Part 1
Session 6 - Building XNA Games for the Windows Phone 7 Platform, Part 2
Session 7 - Advanced Application Development, Part 1
Session 8 - Advanced Application Development, Part 2
Session 9 - Advanced Application Development, Part 3
Session 10 - Marketing Your Windows Phone 7 Application
Session 11 - Working with Media
Session 12 - Final Silverlight Topics and Wrap-Up
These videos are a very good start for all developers who are interested in Windows Phone 7 platform development.