If you startup Windows 7 beta and press F8, which used to take you into ‘Safe Mode’ in prior versions, the only option you have now is a ‘Repair Mode’ which attempts to do something to repair your install. While it’s running there is a dialog with a Cancel button on it. If you press it it says ‘The repair operation cannot be cancelled’. Hmm – that’s useful. A bit more polish needed there I think.