CYMK was a wordpress theme I did for my blog, previously named novus.volce. It was the second experiment with CSS borders and transparency, back when it was less common and  more experimental (and you had to use ie-pngfix).

Here is a demonstration of the transparency in action. The idea was that the sidebar is less important than the blog posts, thus the content is dimmed until mouse hovers over the section. The transparency also stacks, to differentiate the sections of the sidebar.