One user on that thread (I read every page) reported that it didn't work for him, but there weren't really any specifics. There is speculation that this revolves around region coding of the BR drive. It seems PAL users have more successful downgrades with the modified PUPs.
I didn't read all 5 pages so far, but I see the word Master Key being thrown around on here. Did we in fact find the PS3 Master Key? If so, why are we not digitally signing our homebrew and testing that instead of downgrading?
As the playback problem could be due to the modified 3.41 pup file, has anyone tried downgrading to an earlier firmware and then updating to the OFW 3.41, wouldn't that then clear up any issues with the blu-ray playback??