The only post written so far is by Steven Sinofsky, President of the Windows and Windows Live Division of Microsoft. However, he does mention that “As a team we’re all going to participate—many of us will author posts”.
As to content, the first post doesn’t offer anything new about Windows 8, instead being primarily an introduction post. However, Sinofsky does mention similarities to the Engineering Windows 7 blog, which was updated quite consistently throughout the Windows 7 development process and allowed for quite a bit of community feedback. Hopefully the B8 will provide the same levels of community involvement.