The capabilities of Google Earth and Maps would make for a killer travel guide. There's one problem, however. LCDs don't look so great outdoors in the sunlight. The transflective screen would make such a use feasible, comfortable, and possibly slick.
You also need a cellphone connection to use google maps/earth. If you're exploring a city, i think the phone form factor is more convenient. If you're out in the wilderness, you probably don't have an Internet connection.
Google Maps relies (currently) on a connection, but there are plenty of map applications for iPhone and Android that will let you pre-download maps and then track your location via GPS.
