If someone attacks while you're online, saving up to buy something, and gets the gold, then fine. That's the game.
But when they sit there, spying constantly until you've saved that gold up again and steal it a second time, that grates a little.
Third time starts to p*** me off.

So I say there should be a time limit on how long you have to wait to attack the same person again, and I'd suggest 1 hour.