Probably a silly question, but are you running amdcccle as root?
If you're already doing that, maybe I can still help. Here's what I've got:
Graphics card: AMD Radeon HD 6670 (vendor: ATI Technologies Inc)
OS: up-to-date Ubuntu 11.10
I'm using the ATI proprietary driver(s) right now. The open source drivers were working for a while, but my desktop broke with a recent upgrade, so I switched to the dark side.
Here are the basic steps I followed:
mkdir catalyst && cd catalyst
sh ./ati-driver-installer-11-9-x86.x86_64.run --buildpkg Ubuntu/oneiric
sudo dpkg -i fglrx*.deb
sudo aticonfig --initial -f
Once I rebooted, I had to do this to configure the dual-head setup:
Note that sometimes amdcccle crashes, but it still seems to set up the dual-head properly. I have to re-run amdcccle every reboot for some reason. Luckily I don't reboot often, and when I do rebooting is pretty fast.
Anyway, you've probably done something similar to install the AMD/ATI catalyst driver(s). The steps are generic and covered in multiple tutorials.
My xorg.conf looks very similar to yours. I've got a dual head too, but one of them is rotated to be a tall/portrait monitor.