A set of 9 sub-domains have been created with the goal of speeding up the delivery of the various menu images around the site.
All images are cached on the server and depending on which type of image is requested, it will be delivered by the appropriate sub-domain.
This is a part of CSS Menu Builders attempt in following the best practice rules set forth in an article on the same subject by Yahoo, a link is provided below.
In the future it would be cool to add all the static menu images to one file, as this would drastically decrease the requests made by the site, but there is still some way to go, before this is even attempted.
Headers are set for the images, so the first time, it might take a little time to load, but then they should be cached in your browsers as well. Headers are set for 1 week and then they should revalidate.