The program changed recently. It is 2% under invoice now, however most of the sites have not updated their info to reflect that. I got mine for 2% under invoice through Leave No Trace (http://www.lnt.org) last October. I thought it was just for invoice as well, but when I got my paperwork it all said that it would be 2% under. I asked the salesman at my dealership about it when I went in to order the car I wanted and he said he would call and check on that. He called me the next day and said the program had indeed changed and I would be getting the 2% under invoice deal.
You can also check out this document here: http://www.legacygt.com/forums/attachment.php?attachmentid=24228&d=1157857078, found in this thread: http://www.legacygt.com/forums/showthread.php?t=42194 . Joining one of these organizations puts you in the "VIP Partners Program" category of that document.