Because I’m a blogger, and I also have an eye in web design, I find it important to have a clean looking blog design just as much as having interesting, unique content. There is also the argument that with many people reading blog posts through RSS feed readers, most of us don’t see what the blog looks like, so why would it be important?
First impressions are important, and a clean, easy to navigate blog design is a deciding factor on if they will subscribe to your blog or not.
Personally, I like blogs that have blog posts on the right side, with a side navigation or side bar on the left. This is because most people read from left to right, left being the important thing on your blog, which is content, followed by your sidebar. I think of the sidebar as the area where the reader goes next after they think the blog post is interesting, exploring the rest of your site.
If possible, you should always format your blog posts in a way that the reader will have to go to your actual blog if they are reading it in an RSS reader. That way they can see your design and possibly go to more posts, being that they are already on the website.
Remember, keeping it simple usually always works.