In the iOS 5 betas, OTA updates resulted in a notification of an available update. It remained up to you to choose to let it go ahead or not.
Will thiss remain the same? My guess is yes, as there could be too much liability exposure pushing lengthy updates and reboots without the user accepting/acknowledging the action. One 911 call not able to occur because of a mistimed upade push would be a huge black eye for Apple.