We seem to go through this dilemma every time a deal like this comes up, and there is always a divide in people's views about the ethics of taking up such an offer.

The $25 Starwood Rate thread has plenty of examples: http://www.flyertalk.com/forum/Forum74/HTML/002866.html

So before this thread degenerates into page after page of "you're a thief" and "no, I'm not -- it's their fault for publishing the rate and relying on technology", try visiting the old thread.