I don't think that outweighs the evidence from Language Log clearly showing that "which" has been commonly used interchangeably with "that" in good English for centuries. This was linked earlier in the thread. Personally, I'm going to go with Dickens and Melville and Orwell (and statistical evidence) over a blog I've never heard of.
On the contrary:
http://www.writersdigest.com/online-editor/which-vs-that