I mined using CGMiner on a GTX 680 and it worked fine though the hashrate was abysmal (110Mhash/s). Ultimately I was doing more damage to my graphic card and spending more in electricity than I would ever hope to recover and then I stopped. 
Yeah, my card is only getting like 50-60 MH/s on GUIMiner. Hoping to build a legit rig soon though... I just figured that CGMiner is better (since everyone says so)