We evaluated our image specs and settled on PNG-8 at 256 colors. If you are running the most beautiful Web site in the world, you may need really fat JPEGs.Otherwise, smash those things in Photoshop. They are a huge chunk of the data your servers are passing. A little optimization here can go a long way.
Some of the tactics involve infrastructure, some are basic housekeeping, and some are still in the works, but overall we’ve found that optimizing site performance is an ongoing initiative that you never entirely master.