From a Costco monthly email:

Costco members will receive exclusive summer savings of up to 25% and a $25 nightly stay credit at participating hotels for travel through 9/12/10. Must be booked by 9/9/10. See full terms and conditions for details.

North America Andaz, Grand Hyatt and Hyatt Regency Up to 25% off the Hyatt Daily Rate and a $25 nightly stay credit

North America Hyatt Place and Hyatt Summerfield Suites Up to 15% off the Hyatt Daily Rate

International Andaz, Grand Hyatt and Hyatt Regency Up to 10% off the Hyatt Daily Rate COSTCO

At the time of booking, request offer code "COSTCO."

I booked a couple of stays, one GH, one HR, gave me best rate on the website and $25 per night credit.

Terms and Conditions

Offer valid for Costco members only and must be requested at time of booking. Offers valid for reservations booked 5/7/10 to 9/9/10 and stays 5/7/10 to 9/12/10. Discount at participating Andaz, Grand Hyatt, Hyatt Regency, and Hyatt hotels and resorts (“Full Service Properties”) in the U.S., Canada, and the Caribbean is up to 25% off Hyatt Daily Rate for the room type requested at the time of booking. Park Hyatt hotels are not included. Discount at Hyatt Place and Hyatt Summerfield Suites is up to 15% off the Hyatt Daily Rate for the room type requested at the time of booking. Discount at participating Hyatt properties outside of the U.S., Canada, and the Caribbean is up to 10% off the Hyatt Daily Rate for standard room type only at the time of booking. Offer at Full Service Properties in the U.S., Canada, and the Caribbean also includes a $25 per-night hotel credit that may be used at the property on eligible charges posted to your room bill, but credit may not be used on room rate, taxes, gratuities, alcohol, service charges, and resort fees. Charges must be posted to your room bill to use hotel credit. No refunds for any unused portions. Guest must present valid Costco membership card at time of check-in to qualify for the offer. Reservations are subject to availability and must be made in advance. Offer not valid for groups or convention and may not be combined with other promotions. Additional guests and room type upgrades may be subject to additional charges. A limited number of rooms are allocated to this promotion. Promotional blackout periods may apply due to seasonal periods or special events, and normal arrival/departure restrictions apply. Hyatt reserves the right to alter or withdraw this program at any time without notice. Hyatt Hotels & Resorts® encompasses hotels managed, franchised or leased by subsidiaries and affiliates of Hyatt Hotels Corporation. The trademarks Hyatt,® Hyatt Hotels & Resorts,® Park Hyatt,® Andaz,® Grand Hyatt,® Hyatt Regency,® Hyatt Place,® Hyatt Summerfield Suites™ Hyatt Gold Passport,® and related marks are trademarks of Hyatt Corporation. ©2010 Hyatt Corporation. All rights reserved.

Travel purchases are not included in the Executive Membership 2% Reward program. Seasonal surcharges, availability, blackout dates and restrictions might apply. Cancellation and change fees might apply. All prices are in U.S. dollars. Costco Travel disclaims liability for any inaccuracies or typographical errors.