One of the demos that got people (especially ones not currently using Microsoft technology) excited at the MIX conference a few weeks ago was a demo that Shanku did showing the Atlas Client-Script Libraries working within a PHP web app. The Atlas architecture easily allows this, and Atlas can be integrated into any existing server framework environment.
Shanku just posted his Altas w/ PHP sample on his new blog, and you can check it out here. For pointers to other Atlas information please check out my previous post here.
Hope this helps,