Clarification: Let me clarify first: By double-click I mean clicking something twice but not in a quick succession.
So here is the question/suggestion: Usually on the web applications, designers have two choices when it comes to potentially dangerous actions: A confirm popup/overlay/dialog box or providing Undo.
Example: For example, if I wanted to Delete an email in Gmail I can do it quickly, but then I can undo the action until I move away from that page. On the other hand, on iOS, when you delete an app, you have to confirm this with a popup.
I find the popup confirmations annoying, especially when dealing with multiple actions in a short period of time. I also think Undo does not apply to all situation.
For example, if I give my users an option of "Send" for an email, I'd have to send it "now" and undo doesn't make sense once the email is sent.
Suggestion: So here is what I'm thinking: Use a Send button that changes to "Sure?" and performs the act when clicked again.
The difference between this and a popup is that the button goes back to "Send" after a timeout, unlike the popup which blocks the UI and needs an answer either way.
What do you think? What do you think about this approach?