Alright, Just tested on 1.0.5.2. I didn't follow the instructions to the letter, I installed the kexts then fixed the permissions, then rebooted, I get a blue and yellow line down the screen and it wont boot now.
I'm not if it's because I dont have 1.0.5.6 like YannickD does or whether I need to install a Radeon HD package "found in trial 1"? as it states in the instructions.
@YannickD, can you give us a low down on what you did to install it.
Update: Tried again using Radeon HD Package and it made it a little different, screen goes entirely blue and it won't boot. I can try 1.0.5.6 tomorrow.