A blog is a promotional medium and a communications platform. And in order to really monetize a blog, you have to ask the question: ...What is your real product? What is the thing that you can provide to others in exchange for some of their money?
Don't just plaster your blog with banners and contextual ads. Your blog has to serve a purpose, and be of value to your readers. There must be something you can help them with, a solution to a problem, anything that is of value to them.
Your product should be something which is valuable to your audience which they will be willing to fork over a little money for. When you have that, your blog is a promotional medium for an actual business.
The REAL answer to full-time incomes from blogs is to answer that question: What is my product? And if you don’t have one, you need to create one.
After reading that guest post, I followed the author to his blog and am really glad I did. Some of the posts are insightful and reading them is a good use of your time. For me, the biggest take away is this: Write for the blog you want, not the one you have.