I was almost not allowed to board yesterday on an AA itinerary, although my first check-in was at PHL, where they wouldn't have ever come across the TWOV. In the timatic database linked in the wiki it didn't mention anything about it, nor when the agent pulled it up in her database. Luckily I had printed the FAQ from the Chinese Embassy website and that convinced her to let me board.

Arrived at PEK last night (after a nearly empty J cabin, which made for a wonderful AA flight) and went into the regular immigration stalls. My flight back to the USA routes from PEK to NRT, and I had the AA agent print me out a receipt, on AA card stock, showing the entire itinerary and how much I paid. The immigration officer took one look at it, called another agent who brought over the special stamp, and I was on my way. I've never been through Us customs that fast!

Anyway, just a data point for everyone from my experience. T3 is beautiful by the way!