Simon Willison has a post up called Maintainability, a.k.a. the CSS elephant.

What’s needed is a well understood set of techniques for writing maintainable stylesheets. I’m interested in collecting advice on this, especially from people who have tackled this problem in a situation where more than one person has to work on the same CSS code. I’m particularly interested in ideas on how to best split up a large set of rules over multiple stylesheets. If you have any tips, please post a comment, write it up on your own site, e-mail me or add it to the wiki page.

I can understand the concerns, but my experience is that the modular CSS approach is a sufficient solution. Limit the universe of css styles affecting a particular page, and the complexity tends to stay managable (assuming your page structure is clean and you’re reasonably well-versed in selectors). David Hyatt’s notes on Good CSS at Mozilla.org are also a useful, particularly due to Hyatt’s insight into performance of CSS selectors.