Well, just to clarify, I'm in South FL.
When I first signed up with comcast, I did have my IP changing a lot, but then realized that I hadn't cloned my main machine's MAC into my router.  After I did that, life was good.  (I figured they must do some kind of hash on the MAC to select an IP)  Then today I'm trying to get to my box from work, and it doesn't respond..come home and find my IP changed from 66.176.61.x to 66.176.63.x.  
I pretty much don't download anything big, so no idea if the claims about increasing download speed had anything to do with it.  Just thought it was curious that my IP would spontaneously change.