Re: @cyke1
"Imagine buying a car which, by factory default, gives you about 5 mpg"
That analogy doesn't work. What might be more accurate, is to say you buy a car, and in the fine print you didn't read, allows random strangers to temporarily sit in for a ride. That is, you notice people randomly come in for a ride, and randomly leave again.
Additional fuel consumption might be a bit hard to claim, because as I understand it, they don't count that additional bandwidth towards your own plan. Additional power? As above, good luck with that, you're talking fractions of cents.
But what you WILL notice is there is less space, thus carrying capacity in your car - at random intervals. I don't know how or IF the Comcast hardware prioritises the traffic to the actual owner rather than the "borrower".
I don't remember about Comcast, but I do remember this similar thing happening with a number of carriers. I'm quite sure it's in the contract somewhere - even if the bastards had to bury it in a sub-section translated from Swahilii.