WalkScore.com is a website that offers great information about which neighborhood/city is more walkable than the rest (San francisco was #1 and Seattle was #6). It does it as a mashup with Google maps to show you the shops, restaurants, schools, parks, etc. within walking distance and calculates a walkability heatmap. It is available on US cities only so far. It would be interesting to see comparable data of other cities around the world.