I took the Z14 sleeper train from Shanghai up to Beijing, and very impressive it was too - I shared a four berth compartment which was spotlessly clean, spacious with quite a lot of storage space. I even got an airline style meal soon after the train left.
Unfortunately I didn't get much sleep on the train, as one of my bunk mates kept getting text messages all through the night - he obviously didn't know how to set his phone to silent mode. However I did get the last laugh, in the morning he opened up his case, and a bag full of seeds had split, and distributed its contents inside the case!
There are about five sleeper trains that travel between Shanghai and Beijing every night, and they all arrive in Beijing between seven and seven thirty am - there was a huge sea of humanity flooding out of Beijing station!