I have an upcoming post explaining how Groupon works, but in the meantime you might be interested to know that for today only (Thur. Aug. 19), you can get a $50 GAP giftcard for only $25. This is one of those deals that I wouldn't go out of my way for, but if you already shop at GAP regularly, it's like getting a free $25 store credit.
The card expires Nov. 19, 2010 and is valid in-store only. Not valid at any Gap Outlet, Factory, Generation, or online.