After reading this wonderful story about a family of amateur photo-detectives in New York City who worked long and hard to return a lost camera to an Australian tourist, Chris Savery made a smart suggestion: Try putting your email address someplace unobtrusive on your camera, such as inside the memory-card bay door.
That way, in case some good Samaritan wants to return your lost camera to you, they'll have an easier time doing so.
UPDATE September 16th, 2008—Very sad, because it was a lovely story, but the link had been broken now. It was about a family in New York city who worked long and hard to return a lost camera to its owner in Australia. Oh well—the advice above is still good.