An interesting question to ask anyone, and now thanks to World66 , you and your patrons or anyone else can create a visual map to answer it! World66 is sort of a real world Hitchhiker's Guide to the Galaxy, with people submitting information about the places they travel. To submit content you have to login, but you can browse to your heart's content anonymously. The My World 66 section  is where you can create the cool map of countries you've visited (or countries you'd LIKE to visit). Creating maps also requires no login.
Here's my map. I seem to have completely overlooked the southern half of the world. *sigh*