I have been using my OSM viewer for a while now both on the desktop and on my Windows Mobile phone. The two versions have interface differences, but share much of the code.
The mobile version uses my phone's GPS for several things:
centering the map
recording where I have been in GPX files
uploading my current location to my web server so my wife can see where I am
It can also download my wife's location so I can see when to head downstairs to be picked up.
I am planning to package this software for non-programmers to try on their own desktop and/or mobile device, I just need to think of a good name for it...