It’s official, starting January 1, 2013, Beijing will allow transits to a third country to be visa-free for 3 days (72 hours)! This is very similar to what China offers in Shanghai, but in Shanghai it’s 48 hours. You’ll get a stamped 3 day visa upon arrival at immigration and confirmation of your transit.
Yesterday I saw a news release stating that Beijing may allow 72 hours visa free visits.
Shanghai currently allows a 48 hour visa-free transit for passengers coming from outside China to another country via Shanghai. I took advantage of this twice last year flying from HKG to the USA.