In Shanghai I found that ssh was blocked at the protocol level so even running sshd on port 80 doesn't work. I don't whether this is widespread or whether it was our hotel in particular that was blocking it. Regardless, I found a workaround using httptunnel.

On a server outside China:

sudo apt-get install httptunnel
sudo hts -F localhost:22 80

On your client machine:

sudo apt-get install httptunnel
sudo htc -F 22 my.server.com:80

Now you can use ssh to your hearts content:

ssh user@localhost
scp /some/file user@localhost:/some/file
darcs push user@localhost:/some/repo

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