Theme roller is a cool idea, but the CSS it outputs has so much cruft... It's like they forgot about the cascading part.
It could learn a thing or two from YUI CSS here.
Also, I find the themeroller a bit clumsy, spitting out whole zip files - rather than just little my-theme.css files.
unfortunately much of themeroller's flexability depends on images. maybe more CSS support among popular browsers and more consistent CSS support will make it possible to achieve more with less images some day (hopefully none some day)