Gaia GPS recently developed a Burning Man app, iBurn 2010, a free and open source app that works across all iDevices. The app serves as a guide to the events, campsites and art at the Black Rock Desert festival. Those worried about getting service in the middle of nowhere need not fret. It's meant to be used offline and caches maps and info directly onto your device, along with any webpages viewed via the app.
Gaia GPS recently submitted iBurn 2010 to Apple for review, but the impatient can download and build the app from code provided on the Gaia site.