I have just signed up to the full Sky package,i.e. TV Sky+ Talk unlimited and base broadband.I have not had any problems and the change over and service is good. Plus the phone package is cheaper than BT. The only down side is that i only get 2meg on the broadband on the phone copper wire delivery system,but the distance from my exchange only allows me up to a max of 3meg no matter what Sky broadband package i have.
You are right the Virgin Media cable system is faster and better but you have to pay for it. So basically i am happy with what i am getting from Sky. I thing Virgin were just trying to scare you into not cancelling their contract. Go ahead and move as my Sky broadband has never gone down yet.