Virgin users hit by broadband crash
http://www.guardian.co.uk/media/2007/dec/18/virginmedia.digitalmedia

Last night cable operator Virgin Media's broadband and Video On Demand services crashed, leaving an unspecified number of its 3.6 million customers temporarily without facilities including Internet access.
This problem occurred during routine maintenance, however only customers in the North West - Yorkshire and the midlands were affected. The majority of customers did regain their service shortly after midnight. But Virgin Media stated that it was difficult to estimate the number of people that were affected, partly because it depends on what time people were online.

Though this may have been a one off, it could occur again which would then cause customers to switch Internet provider. As it is Virgin media have tough competition with rivals such as Sky and BT.