Hi Emily, I've been doing some research about this as I'll be transiting without visa through Shanghai on an upcoming trip. According to the Chinese Embassy in DC, Shanghai is the only city where you could leave the airport while transiting without a visa. For Beijing, you do not need a visa to transit between flights but you're not allowed to leave the airport.

Tripplanner001,

I have seen the same information (about 48 hours where you can leave airport in Shanghai), which is why I had assumed (before seeing the TripAdvisor Forums) that we couldn't leave the airport. To be honest, I was really surprised that the idea of 24 hours in BJ was even being discussed. Here are the two links that seem to support the notion:

1) http://www.tripadvisor.com/ShowTopic-g294212-i2147-k5289740-o20-Stopover_permit_transit_stamp_in_Beijing_INSTRUCTIONS-Beijing.html#44659273

2) From the IATA website:

Visa China (People's Rep.)
Visa required.
Passengers transiting only are exempt from holding a visa when:
Holders of confirmed onward tickets for a max. transit time of 24 hours. Transit incl. two stops, with a total transit time of 24 hours, within China (People's Rep.) is permitted.
Nationals of USA are not permitted to use the two-stop transit within China, if transiting through Tianjin (TSN), Weihai (WEH), Wuhan (WUH), Xi An (XIY) or Zhengzhou (CGO).
Nationals of USA holding confirmed onward tickets for a max. transit time of 48 hours, provided arriving at and departing from Shanghai Hongqiao (SHA) or Shanghai Pudong (PVG).
All transiting passengers are subject to a check by immigration officials.
Leaving the transit area is allowed.

Any thoughts? This is so confusing!!!!

Emily, I haven't seen the TA information until you brought it to my attention, but the IATA information seems to match the information I received at the Chinese Embassy.

The above reply is incorrect. While the policy says you cannot leave airport, but that is not enforced and unenforcable. Nobody can or will stop you from leaving airport and visit the city. Tonnes of people do it everyday at various cities.

The only risk is if something bad happens during that time and you are questioned by police, or if you ended up missing the flight, etc. You can decide if you want to take that chance. But no one will or can stop you.

Ok, I think I'm confident in making it work. We will have someone meet us at PEK and bring us to the Mutianyu section of the Great Wall and bring us back in plenty of time for our 4pm flight. Thanks to all for your help!

Hi, Emily, as persons in immediate transit who, because of force majeure, are unable to leave China by the original aircraft within 24 hours or have to leave China by other means of transport.

Well it looks as if your (and my) problem is solved as of this week:

http://www.wanderlust.co.uk/magazine/news/72-hour-visa-free-stay-beijing

We too are flying through PEK (in December) and planned to meet our friends for dinner in the city during our 7 hour layover.

This 72-hour exemption has been talked about for a while but not in place. It may not be for a while actually.
The "official" rules say that you can leave the airport on a transit. You need to find the proper desk, show your onward tickets and get the transit stamp in your passport.

I don't understand the post above and the reference to a third country. Of course that "third" country can be your home country. The OP fully qualifies.
In addition, as an update, both Beijing and Shanghai have announced that they will finally extent the visa free transit to 72 hours as of January 1st for passport holders of certain countries. Here is the list of countries that qualify: http://www.wcarn.com/cache/news/22/22734.html