400 yards.
Not because I am lazy. More because where I live in Denver and where I spend a lot of my time it isn't always practical to walk.
- weather freezing in the winter, boiling in the summer
- lack of sidewalks, street crossings, etc
- crazy drivers who don't know what pedestrians are (target practice)
- time, a cop out maybe but when time is short....
My drive to work is 2.7 miles, and in reality I should be able to walk it, though I just did 3 miles on the treadmill last night and doing that in an hour builds up quite a bit of sweat and with no showers etc at work... eww. Also as I am oncall every 5-6 weeks at least that portion of time is not practical, let me stop on the sidewalk and get out the laptop

. Another issue, although my driving distance is only 2.7 miles, the walking distance is otherwise as you need to take a detour of through a statepark and it is not very direct.
During the winter the sidewalks are frequently covered in ice as it is a main road with no businesses/houses along said road so the sun is the responsible party to melt the ice, until it gets real bad and the local council gets out and clears it up a bit.
Back in Australia I never owned a car, my parents and I shared one car for about 5 years before I moved to the USA, walking & catching the bus was the norm. Also the weather in Sydney was better for walking in general.
Ultimately it is a personal decision on what suits your needs best. I would prefer to drive to work and spend about 10-15 minutes driving than 2 or more hours walking, walking doesn't add any value to my day as I would lose so much time from it. Yes I have a treadmill at home for walking, but I also have it in front of the tv so I can wtch my shows and get my exercise at the same time.