Just a follow up to my original post on my 72 hour TWOV entry at PEK. Just went through passport control as per normal, no real issues except that the officer and his counterpart looked at the two stamps as if they had never seen them before. The officer then starts flipping madly through the pages of my passport to see if I had a visa (I do - four of them, all expired). They cheered up substantially when I told them that I came in on the 72 hour status - passport stamped and - amazingly - returned with a smile!

Object lesson when leaving - be sure to tell the officer that you are on the 72 hour status (at least until the end of the month), will probably save you many quizzical looks.