I grew up in a huge subdivision just outside B'ham AL (I moved away when I was 12), but like others, my bicycle was my ticket to roam. My neighborhood was probably 1-1/2 mi square, and I was exploring its limits at 8 and 9, but by the time I was 10 and 11, I was far surpassing its boundaries!
My cousin, who lived 3 or 4 miles away and I went all over that end of town!
We would go exploring some new woods or a creek or whatever, then when we got hungry/thirsty, we would go to the local construction sites, collect the returnable soda bottles, and turn them in for gum, candy, drinks, etc.
My kids? No way - their mom would never hear of it! Until they were driving they never got more than a few blocks away (that I know of!).
Yes, I'm afraid that a combination of freaks running loose on the streets and PC/X-Box/PS3/TV has worked to corral later generations.
Good topic Scott!