I don't read too many blogs, but I do regularly check www.gamedev.net. The front page of this site is commentary about news and events in the game development industry and hobby world. There is a way to post comments by members of the community, so I feel it constitutes a blog.
The web site has a membership system complete with a forum, so each member has its own preferences. In those preferences, the member can choose a particular layout when viewing the site. This allows the users to customize their viewing experience, ensuring that they like the style of the layout. This feature alone makes this blog/web site a very well designed.
Mostly, the "themes" change the colors of things, and not the positions. This is still a great thing because different color combinations and contrasts are better for certain people. Additionally, different monitors are better at displaying certain colors.
Each post is seperated by a visually different horizontal bar, so you can easily know where each post starts and ends. For long posts, there is a "Read more..." link which contracts each post into a smaller amount. This reduces the "wall of text" approach where each post takes up a LOT of vertical space.