It appears AmEx is going into some rewards point arrangement with Marriott (and Hilton) from the following press release I received:

"Have you thought about how you are going to spend all those Amex Membership Rewards points you racked up over the holiday season? Now you can book stays at any Hilton or Marriott hotel, our newest Amex Membership Rewards partners.

Using your Amex Membership Rewards points you can enroll in Hilton's or Marriott's reward programs and then redeem for free hotel stays at any of their combined 4,200 locations worldwide. But that's not all, transferring your Amex Membership Rewards points into one of these programs also gives you access to a number of other choices including flights, cruises, car rentals, dining certificates and theme park passes.

When you use your American Express Card to pay for your stay at a Hilton or Marriott hotel, you will earn both Amex Membership Rewards and Hilton or Marriott reward points. This will enable you to redeem hotel stays even faster.

Hilton and Marriott are two great new choices in the Membership Rewards program, says Alan Stark. Cardmembers can redeem for more than just hotel stays and they can earn more reward points faster. Hilton and Marriott join the growing hotel category within Amex Membership Rewards, which includes Starwood Preferred Guest, Crowne Plaza, Holiday Inn, Holiday Inn Express, Radisson Hotels & Resorts and Fairmont Hotels & Resorts. "