If you have a high-traffic site where the difference between reading a 6kb compressed php-script or a 8kb formatted php-script makes a huge difference, this cms isn't right for you anyway.
Honestly, I've used CSS for as long as I've been slicing web pages (which is now a couple of years) It'd probably cost me more time designing with tables than with CSS. Once you understand the principles behind it, it's not that hard... (for me it feels like a lego-construction snapping together when a design falls into place)
On the other hand, a professional designer often needs to know how to design with tables as well as it is practically the only way to design an email newsletter decently.