Installation worked fine, but got soon problems with the display on my machine with an AMD APU (in my case A8 3850). The Desktop was nearly unreadable but fortuntatly system was still in function.
It seems to me, that the additional proprietary ATI grafic driver offered for Installation by mint 12 / Ubuntu is an old

version.
For me this way worked to solve that grafic problem with my AMD APU. Zero guarantee that it helps in other ATI problem cases !!! Just a hint what helped me:
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Open Synaptic and search with the keyword fglrx for any existing installed fglrx file. Delete with Synaptic any existing old fglrx files . (If there are not any fglrx file installed it is good -> continue with ...open firefox...)
restart the machine - in my case grafic looked now big and and in wrong resolution - but system worked.
Open firefox and google for amd grafic support or go directly to
support.amd.com/us/gpudownload/pages/index.asp
and download from there the latest version of ATI Catalyst after checking through the offered question boxes on the page. My values for example were:
Destop grafics
A-series APU
A8-38xx APU (i ignored in that case for security reasons the option: "Auto detect and install")
Linux x86-64
Go the the downloaded file in your file manager (in my case in home/download) right click and make it under rights (German Zugriffsrechte) executable by marking the little box for it.
I restarted my system after that but think it is not needed to restart.
Double click on the now executable downloaded file. In my case a box with a running script opened and after a while a new window popped up, which offered "Installation".
Click on the Installation option, say ok to the legal BS and let it install. Stay a bit patient and watch the total progress bar developing. After this is done restart the PC and

all should work in right grafic resolution without doing anything more and with the feeling, that you got the best available grafic solution from the producing company AMD itself.
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I am a layman. But I like to suggest professionals and developers: please check out: which Catalyst version is downloaded by the function additonal driver or proprietary driver available (forget how it was called) - that one what pops up after a while after restarting a fresh installation. My guess is, that there is an old version downloaded, which does not work with the relative new AMD APU. May be change to the latest ATI Catalyst version at that point can save many AMD users with new AMD APUs some trouble.
Sorry, for rusty English, my mothertongue is German
