I have had many games with zoo lock where I don't need curse of rafaam in my hand. That being said, I've lost a few zoo lock games that would have been won with this card (specifically freeze mage left at 1 hp through 2 turns of ice block-ness. -.-) I don't think it happens enough for me to pop that in there though.
I actually played Curse in one match, but I never saw my opponent take 2 on any turn where I hadn't just played a Curse, so I wasn't sure if it was working like I thought it would. Glad to see confirmation that it does indeed work.
Other cards that get noticeably better in this Brawl? Deathlord takes forever to punch through with chickens, and whatever his deathrattle summons is permanently out of your opponent's deck. So even if he "backfires", you're still winning in the long run (and if he pulls a Chicken, you've actually helped your opponent long-term but won short term). I've also really loved Undercity Valiant: combo is a lot easier to trigger here and 1 damage is worth more than it usually is.