We are currently optimizing the backend performance. With Firebug we could get all requests for a page and optimize the caching.
First a result with an empty browser cache. It loads about 60 files and takes some time. Because some of the images are module files and can be outside the document root, they need to be send using a php script.
A second click on the same button shows a nice result. Most of the files, including the module images, are cached. Only 13 requests for the page now.
We are still trying to improve that result. But I think it is a good start.