[wizofaus]

"almost always" - agreed, but the specific case where your application has clearly gone into a temporary mode where no user interaction is permitted (other than perhaps "cancel") I would think was the exception. But simply adding the disabled attribute to the existing input controls probably isn't the best way to do it if it's an issue with screenreaders etc. Though it's not clear why such tools couldn't deal with it in a better fashion.

I'd also say I'd have no issue with a button showing as disabled provided when you attempt to click it or hover over it, it tells you why it's not yet a permitted action. But again, might be an issue for accessibility etc.