No such thing as bad weather? You must be kidding me.
We're not quite sure that we've got our timing right as far as the weather is concerned. China in January is likely to be bloody cold, and even by the time we get to South America in July, we might find ourselves back in the cold. If we were to do the trip the other way around, however, we'd get Winter in Australia, and hit Beijing around the Olympics.
I think we'll have to live with the fact that the weather will be less than clement at the start and finish of the trip, but that we'll enjoy a good 3 months of Summer/Autumn in Australia, and get a bit of skiing in when we're in the South Island in NZ.
My remaining concern is that, because of the fact that we'll be in China so far off peak season, that many sightseeing options will be closed to us.