Just as an update, the other person who tried would only have saved $4 off of the rate she had already so she turned it down. That's not surprising when you consider that the 50% savings is off of their regular rates and so many deals are available now. However, she did google the coupon and found that you could save a good deal depending on which hotel you use, so it's worth a try.
In order to save time I'll just put out the info, you can all try it and the I'll send them out to the first 2 people who find a deal. Call the hotel you want to book your room at (I don't think it works if you try to input it through the website) and ask for rate plan ID SPG50 when making your reservation. Make sure you save your confirmation number then PM me with an address to mail the coupon to. You have to present the coupon at checkin. Good luck.