I have just noticed this as well. There must be a problem with the Sling servers. In IE and Chrome it sticks at the 'Initializing' and in Firefox it connects to the Slingbox then freezes.
Moderators: You need to get the tech boys working on this urgently.
AndyBoy: As a temporary workaround use the US viewing site http://newwatch.slingbox.com This seems to be working.