It worked for IE 6 Safari Opera 8+ and FF2+.
You should read this:
Gif Compression
It explains how GIF (and other image files) are compressed.
For example displaying the same data in "rows" instead of "columns" reduces the space usage dramatically.
Furthermore you preload all images and there is no delay if you swap images.
Another plus is that you can use one sprite for a "red" design and another sprite for a "blue" design.
However there is one disadvantage:
Most of the browsers cache the image sprites.
So you might running into troubles when it comes to updating the sprite.
