The current CTP for the Windows Phone Developer Tools does not include the final scaling/rotation logic that will automatically handle orientation for XNA Game Studio games. Because of this it can be hard to start working on a landscape game for Windows...

Update: D’oh. I just now realized that Michael beat me to this topic five days ago. You can see his version on his blog: http://klucher.com/blog/expert-settings-for-multiplatform-development . One thing most XNA Game Studio developers are likely missing...