Specifically, it will attract a lot of customers, but runs the risk of reducing customer perception of the value of your product. Sounds like a good match if bargain-seekers are your target market -- your promotion ends, and you're still among the best deals.
But it sounds like a terrible thing if you're selling the equivalent of a Lexus or Acura in your market -- luxury products defined by the perception of their extreme worth/status.
I have used it to buy stuff at high end clothes stores (well Gap - but anything other than $3 black T shirts is high end for me!). If I ever needed more clothes I might go back to Gap, it did get me to go into a store I wouldn't have entered and was probably cheaper and more effective than them putting their name on a yacht race.
If everyone who heard about it on the internet could afford a Lamborghini, no movie star would own one, no matter how fast it went.