Don't see why? All companies do this from time to time.
Virgin have had a recorded message on their lines for a least a month to tell people that this is going to be happening
Was also posted on the service status page here
http://status-cable.virginmedia.com/...?ticket=696009 on the 24th of April
If I remember right Sky had all their systems offline for a week back in 2006 when they changed over their computer management system.