It's also worth noting that semantic markup is not a feature of CSS, it is a feature of HTML. CSS has almost no power if something like a scraper or a reader mode chooses to ignore it. Of course that would be pandemonium and we would never get good results.

I feel like something in the CSS camp that could be highlighted in a "great idea, okay implementation, poor reception" that the OP is going for is print stylesheets. Those are incredibly underused.