Walkscore.com is an excellent website. You can enter a U.S. address and it will give your neighborhood a walkability score on a 100 point scale. The score works by counting the number and type of destinations that are walking distance away. If a destination is within 1/4 mile of where you live, that boosts your score the most. If a destination is more than a mile away, no points are awarded.
As you can see from the picture, downtown Cleveland, Ohio scored very highly on walkability at 95/100. This means it is in the "Walkers' Paradise" range where "most errands can be accomplished on foot and many people get by without owning a car".
Walk Score doesn't take into account things like crime rate or the quality of the sidewalks, but it's still a fascinating way to evaluate a neighborhood. As you can see, many parts of Cleveland (the parts in yellow and red on the map) don't come close to downtown in walkability. These sections are in the "car dependant" or "somewhat walkable" range.
So, what's your walk score? What makes it high or low?