Last time I went there (four years ago) - we flew into St. Louis and then flew the Polar Route over with a stop in Anchorage (had to wait there because no plane noise can be made in Japan before 6:00AM and after 11:00PM) -- then to Tokyo and into Bangkok. I think it was like 18 hours and the date line screws your mind up big time...
I used to fly to China quite a bit. The flight is LONG and boring. The long haul portion of the flight (from LAX or EWR) to Beijing is usually around 13.5 hours. The flight back is shorter by an hour. Of course, you have to add the time it takes from where you live to LA or Newark.
Personally, the time change when I get to China doesn't affect me much. I adjust the first night. The hard part is coming back. It takes me 4-5 days to get back on track.