If you happened to have lost any rolls of film at Burning Man, the staff have a page just for you. All the rolls of film that were found have been processed, and a few of the pictures were posted in the hopes that you would recognize one (or some) as ones which you may have taken.
and follow the pictures link.
Other items lost can be reported or discovered in the lost and found bulletin board as well.
I've been real careful, and haven't had anything go missing on me since my sister's bike walked away from camp in 1998.