20Mbit or 5Mbit?
If you look at various Virgin Media usenet groups, the customers on 20Mbit feeds are not happy with the traffic management that throttles them to 5Mbit/s if they try to use their links at peak times. Those on lower speeds only get cut to half speed, the top speed (paying a significant premium) is cut to 25%. It gives the impression that they've rolled out the service without having the backbone links to support it fully.
It might be a beacon of light in the ISP world, but it flickers rather badly.