Discoe and I went for walks right when I brought her home at 8 weeks. We started off slow, and would just walk up to the end of the block and back and gradually extended our range as she got older. There aren't many dogs on our block, nor do too many people walk their dogs through our area, so I wasn't worried about her getting anything. Still, with the distance that the park (a popular dog-walking spot) was from my house anyway, we didn't end up walking down that far until her shots were all well and overwith anyway and I was sure she could handle the distance (from my house, down around the perimeter of the park and back is around a mile, if not possibly a little more).
We live in a suburb where everything is pretty much crowded into one area. Our high-school, police station, city hall, library, rec center, pool, park, ice arena, jail and middle school are all more or less down the same strip of street not far from my house, so it was ideal for socialization with all the people, vehicles and sounds.