My namesake, Shel Holtz sings praise for the Google blog, and sites what I consider a lame article om PR Week, that lauds Google's blog for giving "a voice to the company brand." I always thought a brand was about how people felt about your company making the comment seem a bit inane to me.
As for Shel Holtz, he usually has a superior eye for quality and I have a hunch in the case of Google's sorry blog, he must have blinked while checking it out. As Mike Manuel pointed out, the Google blog allows no comments, but that's just the start. The blog never links to other companies. It never makes note of anything happening in the marketplace, except when it's Google. Even the linking policy is myopic, connecting primarily to people, and content that are inside of Google.
In short the Google Blog doesn't join the conversation--and with all good deference to PR Week, blogging is about two-way communications bringing companies and constituencies closer together. This doesn't work unless a company uses the technology to enable itself to listen.