Using the undocumented MPTVOutWindow class, Steven Troughton-Smith was able to update his iPhone Doom port to enable TV-out and on screen controller support. Doom on the iPhone on a TV is a pretty big deal to start with, but the bigger story here is that in addition to the TV-out features, he was able to get the touchscreen input and display working concurrently.
Now, if you make an app with TV out support, you can use the iPhone for motion and touch input, as well as an additional output device, which might be useful as a heads up display.
The MPTVOutWindow patch is included in the latest iPhone Doom source. You can try it out by following Erica’s instructions over at Infinite Loop. It amounts to swapping out a couple files, adjusting a few settings, and rebuilding the project in Xcode.