CSS is the second-most-important thing you can master when it comes to web design, right after HTML.
And the capabilities of CSS can be staggering (especially with the new CSS3 standard already making appearances in some browsers).
If you can imagine it, it’s likely someone has already figured out how to do it with CSS.
Many designers, whether traditionally schooled or not, have trouble with composition. I’ve sat with plenty of designers who simply moves things around until they feel ‘right’.
Design is, in essence, communication (I know, I know, I rant about this enough, but this isn’t one of them) but the vehicle for communication is the design. One of the key components in the vehicle of communication is composition, and in design schooling it is something that is taught as something you should feel rather than create logically. This has always bothered me.