Wow Bruce, I was gonna respond to Hachi with a much less detailed explanation (since I don't remember the details) but your explanation is much better than I coulda done with quick google!
On that note, I've used other people's DSL before and it was fine for web surfing but Cable has definately been consistently quicker. Every now and then things may slow down a little but really noticible since I'm not downloading huge amounts of data (movies).
I remembered the 3 mile fule from the central office to the end user, and the closer you are the quicker it gets. Makes me wonder how many COs they have around...
-Dave