In trying to improve my site’s performance, starting with using the YSlow! Firefox extension, I came across the concept of “smushing” images. Smush.it is a Yahoo! service (which is why it’s tied to YSlow!) that optimizes images in such a way as to reduce their size without adversely affecting image quality. I believe I reduced my total image size by about 10-15%, which isn’t huge, but when you’re talking about Web site optimization, every little bit helps. The only thing to be aware of is that sometimes GIFs will get turned into more efficient PNGs, meaning you’ll need to change your HTML accordingly.