While creating a Windows Phone 7 XNA game that uses the accelerometer, I noticed that as I tilted and rotated my phone, the screen orientation would switch from Landscape Left to Landscape Right, this obviously made the game a little difficult to play.
To resolve this, I simply changed the SupportedOrientations property on the graphics instance. By default this is set to a landscape where the orientation changed based upon accelerometer input. Adding the following line of code to my constructor resolved the issue.
graphics.SupportedOrientations = DisplayOrientation.LandscapeLeft;