I just noticed this ad in the Wall Street Journal today, but apparently it has been around a couple weeks.
Earn a $100 Amazon gift card after every two Westin Hotel stays arriving Sunday – Thursday now through May 13, 2010.
This offer applies only to Westin Hotels in the USA and Canada.
Must be a Starwood member to participate and each member may earn maximum 3 gift cards.
It doesn't appear expensive rates need to be used--the best availalble rate qualifies for the deal.
Register by April 30, 2010.