I am seeing exactly the same problem on my machine. My motherboard is also an Asus A8N-E. I'm running Ubuntu Dapper with the 2.6.15.26-amd64-generic kernel.
It used power down correctly under Breezy and powers down fully from other operating systems. -- USB devices are not powered off at shutdown (Dapper, 2.6.15) https://launchpad.net/bugs/42149 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
