CSS sprites are a commonly used technique to decrease page load times. One of the biggest hassles when setting them up, though, is figuring out the coordinates for the images in your sprite. (The other is rebuilding the sprite when you want to add new graphics…)
There’s not much to be done for the latter, but there is a handy tool that makes finding the coordinates painless. Sprite Cow intelligently draws a box around an image you select in your sprite sheet (after you load the sprite, of course) and writes the CSS for it. You can’t get any simpler than that.
I bet the developers could make some good money by making a Mac version and putting it up for sale in the App Store.