As promised, Steve Jenson of Pyra has uploaded developer-preview documentation of the Blogger API 2.0 to a temporary location at the Yahoo group bloggerDev. He says
I’m waiting for a DNS change to propagate before I give it a permanent home. Once that update is finished, I’ll open up access to [an] API Validator [that] will allow you to test API 2.0 clients without needing a Blogger account.
Jenson says he does not consider the API set in stone and is “incredibly open to hearing what people like and dislike about this new API and its datastructures.”