The only scenario I can accept paste-blocking is double-field password creation. At least one should refuse paste, just to make sure I haven't copied the wrong string.

Whilst we're on the topic: I hate stupid input fields that don't ignore whitespace and have a maximum number of characters. So you paste the space-separated number (I'm looking at you IBAN), get an exception because of the spaces, go back and remove them, get another exception, and then realise that the number was truncated due to the field length restriction applied on paste. ARGHHHHHH