eBookNewser has a summary article about this phenomenon. Here’s a snippet:
The South China Post has more: “Some Net users are accustomed to using proxy servers to circumvent the mainland restriction, but the Kindle makes this unnecessary. ‘I still can’t believe it. I casually tried getting to Twitter, and what a surprise I got there,’ a mainland blogger said. ‘And then I quickly tried Facebook, and it perfectly presented itself. Am I dreaming? No, I pinched myself and it hurt.’
More info at the site.
Theres a cool tool for checking whether sites are blocked in China or not here: http://viewdns.info/chinesefirewall/