One of my locals was having a tough time locating the Windows Phone "Mango" Training Kit . Search http://downloads.microsoft.com for mango, and nothing is there. So I thought I'd supply some the direct links. I also threw in a few of my other favorite "mango points of entry" as well.
Note I keep most of this stuff aggregated in the mango section of my screwturn wiki at http://dfwiki.devfish.net/technology.Windows-Phone-7-1-Mango-General.ashx?HL=mango .
Windows Phone "mango" Training Kit - compass, gyro, motion sensor, multi-tasking, fast app switching, background agents, alerts, reminders, live tiles, search extras, calendar and contact apis - http://msdn.microsoft.com/en-us/WP7MangoTrainingCourse
Sweet "mango" Samples and Source Code - camera, search extensibility, local db, xna+SL integration, ringtones, sockets, gestures, tiles, notifications, reminders, background transfer, sensor, simple motion, augmented reality http://msdn.microsoft.com/en-us/library/ff431744(v=VS.92).aspx
Updated MSDN API Documentation - http://msdn.microsoft.com/en-us/library/ff637516.aspx
Updated XNA Documentation - http://create.msdn.com/en-us/education/gamedevelopmentt