Motley Fool calls this a customer disloyalty program (http://www.fool.com/News/mft/2004/mft04060908.htm), and GM's dumbest move. I'm not sure about dumbest, although given that the entire page is in images not words...

Still, it is the next logical extension to the 24hr testdrive, or those "get $$ to testdrive a car" promotions.

The next obvious move is that they will subsidize your lease terms for a competitors' car. Yeah.

GM - $250 Challenge