Would there be decent cargo traffic coming from Guangzhou and all the factories in Pearl Delta. I recalled that when I first got my new 24 inch iMac (just newly release) it was sent by air either UPS or FedEx (I know, they have their own planes, but an example of air cargo).

Also if one's ultimate destination is somewhere else in China, the domestic leg intra China is way cheaper than flying out of HKG. So much so that I once seriously considered catching the MTR airport subway to catch the KCR train to CAN. Maybe there's some possibility for traffic in that area.