From the use-in-academia perspective, blogs come in two flavors: personal and authoritative.
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 very rarely be used as sources in academia.
Blogs fall into this category in one of two ways: they are under the auspices of an organization/formal media outlet, or the person blogging is an established authority on their topic and also contributes to formal publications and communication channels.
This means that the person providing the information brings a known reputation, their own or that of the organization/media group they're writing for, and it allows you to evaluate and use the resource as you would an editorial or opinion piece in a published/edited source.
