Virgin Media (ex. NTL) support Linux just fine, despite their claims not to.
Today I helped a friend sign up with Virgin Media's broadband service. He was having trouble, as their front-page at http://activation.virginmedia.com/ does a brain-damaged test, and tells you that they only support Windows and MacOS X and that if you have anything else you'll need to phone them at a pound a minute so you can talk to some idiot until you lose the will to live (or some such).
After a brief rummage, I noticed that if instead of doing what they tell you to do, you go to https://autoreg.autoregister.net/ you get prompted for whether you're signing up for Broadband or Dialup, and on clicking Broadband, you're lead through the sign-up procedure with no complaints about compatibility, and within 5 minutes he was online with his GNU/Linux (Ubuntu) system and Firefox browser.
This makes me wonder why Virgin Media bother putting extra effort into turning users away when in fact the sign-up procedure would work perfectly if they hadn't bothered with the stupid browser test.