Excellent company
I have been a happy residential customer of ICUK/CIX since 2007.
At first they had my broadband while BT Retail had my phone. In 2009 there was a fault on my phone line that BT Retail was clearly structurally incapable of diagnosing. This went on for more than four months. Then the manifestation of the fault changed and it only affected my broadband, so ICUK stepped in. They got it fixed in a couple of hours: apparently a card at the exchange had been knocked out of place. They also helped me prepare my complaint against BT Retail, except that the "Ombudsman" is in the pocket of BT and whitewashed the complaint. Of course I switched my phone to ICUK.
(On Monday I lost my broadband for an hour or so but it came back without any intervention.)