Further to my earlier entry about Slashdot's CSS conversion showing that standards based design is making real world in-roads, Simon Willison is trying to address the question of maintainable CSS.
As a web developer on large web projects, I am concerned about the maintainability of the C# code we write. But the same standards need to be applied to CSS. With hundreds, if not thousands of styling rules applying to a large site, it's extremely hard to dive into a new CSS layout and understand what's going on.
Digital Web tries to address the fact that CSS isn't something that can be hacked together anymore - it has to be architected. But while there are a couple of techniques kicking around to help navigate and arrange your stylesheets, I really think that Simon is correct in trying to bring this issue to the fore. For real enterprise-level acceptance, we need enterprise-level techniques to allow multiple developers to create high quality CSS files.