I've written my first Flash app. It's a remote control panel for SageTV and it runs natively on our Insignia Infocasts (which are Chumbies under the covers). It was a bit of work for me to understand Actionscript and figure out everything to make it work, but I've gotten to a point where I can show my progress. I started off using the Chumby2MPD sample code and the FlashDevelop package for the development. Each button on the app fetches a URL to a PHP script running on my Apache webserver, while passing it the command to be issued. The PHP script in turn issues an xPL message directed to the SageTV xPL plugin, which interprets the message and controls SageTV.
Here's a screenshot of the interface on the Infocast:
And here's a video of it in action.