Unless you use data: URIs and base64-encode the images, which can result in a smaller CSS file than "pure" CSS while still eliminating extra HTTP requests. That depends on the complexity of the image and of the gradient set (or what have you) that would be needed to replace it. Optimization is always situational.
Oh great, I once felt the need of it, but did not it actually existed. I feel though that pure CSS solution would be better, since modifying the colors etc would be easier with pure CSS.
