The Science Blogging Ethics Wiki links to prior posts that discuss the underlying issues of blog ethics. Ryan Somma of Ideonexus has an interesting idea: Blogger Accreditation Standards for Scientific Accuracy. I don't think it's feasible, but it's definitely thought provoking.
The issue he identifies is one of trust. There's general recognition that you can't believe everything you read online. The problem then lies in figuring out what to believe. Science bloggers tend to be an excellent source of information - very often they're a marked improvement over what passes as science journalism and "science by press release". But how can you tell the good from the bad? If you go to a place like ScienceBlogs you are likely to find a lot of good - but even they make mistakes. When it comes down to it, we're all amateurs once we step outside of our area of expertise. Since we all step outside of out particular field of knowledge, simply trusting the blogger is no guarantee that any given post will provide high-quality analysis.
Somma proposes the idea of after-the-fact certification of blog posts - that you could submit posts to a panel of expert reviewers who would decide on certification. It's a good idea in theory, but the problem would be one of finding enough experts. While this would be far less demanding than reviewing manuscripts, it would still require a major time commitment. There would need to be some sort of reward for doing so. There is very little reward in manuscript review, but it's still expected of you as a working scientist. In addition, if you publish, someone has to review your manuscripts. So what would you do to entice reviewers for blog post certification? Maybe when blogging becomes something that you can add to your tenure dossier. Short of that, I just don't think the resources are out there.