From the use-in-academia perspective, blogs come in two flavors: the personal and the authoritative voice.
Personal blogs abound. They are fascinating, amusing, infuriating, and addicting. A personal blog can become well known and significant, but ultimately, it is one person's unedited opinions. These should rarely to never be used as sources in academia.
Blogs fall into this category in one of two ways:
This means that the person providing the information brings a known reputation, either their own or that of the organization/media group they're writing for, and it allows you to evaluate it and use it as you would an editorial or opinion piece in a published/edited source.