This question is very easy to answer if you know why dropbox was blocked in the first place.
* I was living in China, happily using Dropbox.
* Suddenly Dropbox tells me it can't connect.
* Did some digging with tcpdump, traceroute, etc. You know. Nerd stuff.
* Turns out that our of Drop boxes entire IP range, only 1 IP was blocked.
* This IP happened to be the login or authentication server that the client occasionally connects to.
* As it happens, the SAME IP was used for Dropbox website.
* It seemed likely to me that the website was the target of the block, not the login server for the client.
* So I check the Dropbox forum on its website (using VPN) and what do I see there: SONG TEXTS OF TIBETAN NATIONALISTS
Yes, so Dropbox was blocked because some nitwit decided it was a good place to post some pro-tibet/anti-china texts. How do you get unblocked in China? Remove the offending text and change your IP address (or wait a really long time.)