Thanks for the heads up. I believe the deal is done. The Negotiator sent me the link for the $50. It requires a 3 night stay before the end of the year, and must be booked by May 31.
They didn't tell us about that 3-day thing in advance. Like most heavy priceline users, I'm booking one and two night stays all the time, but I'll have to think about a 3-nighter. BTW, unlike some of their other promos, it looks like the discount must be used from your own account, and is nontransferable.