Jimmy Lin is a famous Taiwanese pop star also known as an actor and race car driver. He has close to 14 million followers that read his blog from Weibo: http://weibo.com/dreamerjimmy
Lin wrote in a blog post: “Today I can confirm that the upcoming iPhone 5 will be longer and will have aluminum back like the iPad. With its four-inch screen and thin body it feels about the same in the hand [as iPhone 4S did]. The iPhone 5 doesn’t use the standard 30-pin dock connector; instead Apple put a smaller 19-pin connector.” The blog post also has a collage with photos of the new iPhone from multiple angles.
Although China is well known for its knock-offs and iPhone clones Jimmy Lin’s post looks legit. China is well known to be a source for many major leaks and iPhone 5 could just be one of those.