Personally, I keep a printed multi-page CSS reference guide with me anytime I need to do some work with styling a website. (Actually, this is something I’ve had for quite some time, perhaps since I first started using CSS for my personal web creations a few years ago).
I think there would have to be a good reason for many web developers these days to not be using at least a bit of CSS in their websites/web apps.
It makes sense to use it, especially if you want to be able to quickly switch your look and feel of your whole website.
You can easily one minute have horizontally aligned menu bar at the top of your page, and then using a bit of CSS just change it to a vertically aligned one sitting on the left hand side of your website. And then applying a few more styles you can change the size, the background colour, the font colour, and so on…
CSS is powerful, so use it carefully 🙂