It's CSS Naked Day, is your markup showing?
There's a certain purity to seeing content with absolutely no CSS applied. Raw structure, a focus what the page is really about. It pares away all possible distraction, shows the heirarchy of content. Plus, it kind of reminds me of the early days when my net access was text-only ;) (vt100, dialup).
Running good semantic HTML without any CSS is perhaps the most levelling thing you can do - everyone can use it. Desktop browsers, mobiles, Lynx, screen readers... the Googlebot is pretty big on text, too.
Good structural markup is the foundation for a solid, flexible and maintainable website. You should always pay attention to your markup!