Here is what the Radisson site says about their promotion:
Friday is Freeday
Now through September 15, Fridays are free at Radisson.
Just when you need it most, Radisson® comes to the rescue with an offer you can’t afford to pass up.
Book the Friday is Freeday offer for arrivals between May 15 and September 15, 2009 at participating Radisson Hotels & Resorts and get the Friday night free when you stay two or more consecutive nights, including a Thursday or Saturday night. See below for full terms and conditions.
Book now or call 1-800-395-7046 and ask for the Friday is Freeday offer, because free Fridays won’t last long. Advance reservations are required.
This link will give you all the information. Please be sure to read all the terms and conditions.
A special thanks to the Frequent Flyer.com newsletter for alerting me to this promotion.