About the fglrx blob :
I did a 'plain' install, not generated distro-specific packages.
Multi-monitor is very flaky, again, compared to nVidia's blob. It does work, but misbehaves when I plug in a HDMI display, it needs 'enabling' with a restart of X to work ( the first time ) and so on. Again, not a deal breaker, I'm a technical user, but certainly far behind nVidia's blob.
The 12.6 proper ( not beta ) was tested on Mint x64 ( kernel 3.2 and custom-built 3.4 ), Debian x64 ( kernel 2.6.32 and custom-built 3.4 ) and Gentoo with custom-built 3.4. The default installer completes OK ( as far as output goes ) , the fglr.ko is loaded but neither the installer nor manually `amdconfig --initial` generate a correct xorg.conf file. I had to hack one 'by hand' from the previous beta 12.6, but X crashes when it tries to load fglrx and, frankly, I've given up on trying to make it work, I'm going to wait for 12.7.
In 12.6 ( release and beta ) GPU switching is done manually in CCC. You have a radio group to choose between 'maximum performance : discrete card ' and 'maximum battery : apu' ( or something to that effect ) and the change only happens after reboot. It does work, but it is disappointing overall.
As for the open-source radeon driver, I had to wait for 6.14.4, which is the first one with 'official' Trinity support. I've also tried the latest 'stable' ( 6.14.6 ) but support for my particular hardware is very poor and, the most annoying thing is that it can't shut down the discrete gpu to the effect that the laptop overheats on light video usage.
I'm going to wait for 12.7 and, when I have time, I'll try to do a clean install and test 12.6 stable with 3.4 to see exactly what happens. However, this is a far cry from nVidia's blob that 'just works' and always did.
I understand that AMD is in deep trouble and non-windows driver developers is probably very, very low in the priority list, but it still disappointing.