I'm a priest player only,
one time i was playing against someone who stealed my quest spell; but I also was able to copy the same spell from his hand with those thief cards...
The amazing play I played was that I had a mage secret in hand (cant remember why), the move was this:
I copied my/his quest spell back
I played the mage spell
I attacked and played another minion
the player thought that the secret was Counterspell.. so he played a 1 mana spell to test...
that was it.. next turn i played my quest spell and won... i laughed so hard that day