I switched from BT Business (ADSL) 8Mb, which I got 6Mb, to Virgin 20Mb (Cable).
First I got 2Mb, so I rang there support line (25p min), got through to India, she seemed to know her business, she had me run a few test before arranging for an Engineer to call the next day, it was a loose connection out side, the call cost ?5.00, but refunded in my case.
I now have 6Mb-20MB, depending on the time of day, things that affect this are people using there Cable for X-Box/Play Station Gaming, and TV down loads onto set top boxes.
So far I don\'t regret switching, but wish the speed was more constant, it is however overall faster then my ADSL was.