His blog is updated regularly with well-written posts around 500 words. The posts tie back to several of his main themes which he details in his book. A few examples of his themes are Engaging your Online Community and the concept of Digital Darwinism, where businesses have to evolve their online strategies to keep users coming back for more. He also has a podcast with nearly 200 episodes and does speaking events.
Six Pixels was Joel's first book, and I feel that it was missing some polish. The book is quite long, weighing in at 287 pages. Reading it in two separate sessions (I normally try to read cover to cover) confused me about the point he was trying to get across. The book does not have a main theme to communicate to the user, it has many. This makes trying to keep track of all of them difficult, especially when the book is so long. Each chapter has a central theme that it communicates with backing examples, but the chapters do not flow together as well as they could.
I would add a "how to read this book" section in the beginning of the book. Reading it cover to cover does not make sense, but reading it a chapter at a time does. I think the book would work better as an online strategy reference book than as a normal book. I feel this way because of the abundance of content presented in the book. It could be split into multiple books, with more supporting (and non-supporting evidence) to make the topics more realistic.