In my experience, the key is that the UI makes it clear exactly what you're doing. What I mean is, instead of a button that says "Start Imaging", it should be "Start Imaging of the 12,600 computers this rule applies to". Of course, that's a lot more work for the programmer, so it's never done.
It also helps to have sensible conventions for naming hosts and groups. If you need to select a subset of machines then you are sometimes going to make a mistake as simple is getting a wildcard pattern wrong. Instead have groups with explicit and obvious names that require no memory to understand.
But then that leads to people automatically clicking "Yes" to the "Are you sure..." dialog. Though even I would pause at "Are you sure you want to reformat 12,500 machines including this one?" ;-)
Event that is hardly enough. There should be a physical (well virtual physical) obstacle towards launching a high stakes command.
The system should be able to assess the scope of a task, and ask you to confirm 10 times if it has to, in blinking red dialogs, to make sure you really want to do what you are doing.
Of course, it's crucial that "clicking 10 times" is not the default behavior for any trivial action. Or boredom and the subsequently formed mechanical 10-click habit of the operator will kill the effectiveness of this approach...
