There's a project I'm working on that has a landscape setup. I don't want it to rotate to portrait mode, but it's OK if it auto-rotates to upside-down landscape mode.
I thought about using the accelerometer data to rotate the whole canvas. It looked like it was getting close, but then I got tired and frustrated. The project is an app, so I can just lock the app to landscape orientations. The app would be better with 4-way rotation – so I haven't given up on the idea. But so far, I haven't quite figured out how to smooth out the transition. It should look like it's not moving at all.