I'm curious how many people have shopped around using the 4th night free benefit. Every time I've looked at hotels through citi's portal, they've been quite a bit more expensive than booking through the hotel directly, to the point that 4th night free benefit didn't save much $, at least when it came to mainstream hotels. High end resorts may be different. That's been the Prestige benefit I've (disappointingly) gotten the least use out of that I expected or wanted to.