If you exceed 100GB in a month on BT's so called "Unlimted" package then they can and will cap you to 1Mb during peak times :/. We have this package at our Uni house, it's not hard to break the 100GB limit when there is 5 of you sharing the connection. The service we've had from BT has been appalling.No I'm on the top option so there's no limits to downloads. It's actually back up and working now, even a little faster than previously. I'm guessing just an exchange equipment problem.
Sky do also I believe. We're with them at home and lets just say I'm not a light user and they've never complained or adjusted our connection speed.As far as I am aware, Virgin are the only ones who offer a proper unlimited top package