CSS and CMS
Designing a site now that has to push the envelope of how CSS must be able to tweak the layout, much like CSS Zen Garden but for an ecommerce application. We're also using a content management system, so the interplay of CSS and CMS becomes interesting. I think I can simplify the CMS templates so they only have to reflect business logic, and all the differences in presentation are done in the CSS. Still, it changes how I think about content types. Normally I'd only think about how granular the content types need to be to work in every template. Now I'm also thinking about what I want to appear in separate DIVs too. Not sure if that will end up being more granular or not. Dave Shea posts related thoughts about the relationship between markup and CSS flexibility.
Besides all the usual advantages of CSS, it should be an easier implementation as CSS development is easier than CMS template development. I think.