Perhaps a design blog should be more defined. I see three often separate ideas. Thoughts, Knowledge and Resources.

Places like Design Observer, Speak Up and Ideas on Ideas plus others are Thought blogs. They bring up larger, ambiguous or related topics as they relate to being a professional designer of many trades.

Knowledge sources are the blogs like Not Cot, Swiss Miss, Unbeige, Core 77, ffffound, Coudal(though this animal is unclassifiable sometimes), that serve up current industry news, products and other random nodes many find interesting.

Where most of these blogs mentioned in this post fall are into the Resource category. How-to features, tutorials on making letters look like grass and textures are tools of design, but they are not inherently what I or others would qualify as design blogs.

These sites are valuable resources to even a fellow like me on occasion who doesn't spend most of his day manipulating images in PS. So when I need an idea on how to accomplish something such as this these are places I'd look.

Unfortunately, there does seem to be a lack of interesting and engaging content on many of the blogs. Even the academic ones have become snoozers from time to time. If you really want to start a new design blog, focus on lighting some fires, some which you may not be able to contain.