Comcast (and other ISP's) are notorious for doing throttling they don't notify you of, regardless of what you're paying for. When I was in Chicago I had their increased "blast" data plan and figured out they were throttling us after using it for about 3 months. Called to complain and they gave me the blast option free for a year (it was only an extra $10 each month, so, meh), but they would still periodically throttle it if my roommate was doing a ton of gaming or if we were downloading too many, uh, "acquired" files via FTP transfers.