What happened?
Just proof (forum where it's happened to a lot of people, a letter from sky etc...)
I know it breaks the T&C, but can't see them investing time and money in it.
I couldn't point you in the direction of a forum that has a lot of people on it saying that it has happened to them. I have know idea how much time and money they invest in it.
All I can say is that I changed my modem router from the one that sky provided to a belkin wireless N modem router.
All was fine for about three days, then I noticed that my speed had dropped (not by a massive amount, but I can only get 2.5meg download, so any drop is noticed).
As I was very busy at the time I decided to call them at the weekend rather than straight away.
The next day I received a call from sky saying that I was in violation of the T&C and they would not put my speed back up untill I had changed my modem router back to the one that they supplied.
Almost as soon as I changed back to their modem router my speed went back up just like they said it would.
That said, I have heard of a lot of people changing their modem router and not having any problems, but then, I do work for sky and so might have my account monitored in a different way to normal customers.