My mini is affected, but it is over 3 years old now, only has 2-3gb ram MAX anyway, so it is time to move it on due to other reasons anyway.
It currently runs Lion server (test/toy box), I might run Linux or FreeBSD on it instead, or just stick with Lion.
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I'm starting to wonder if Apple deprecated the older machines simply because they wanted to stop having to port older video drivers.
Pretty sure this is on the money. Its quite possible they subcontract out video driver development to the hardware OEM, and the OEM no longer maintains the code (or the cost to re-write for 64 bit OS X kernel was excessive). Do the affected video cards get new windows drivers on a regular basis? I suspect not...
Apple are not a 3d hardware driver company. They integrate and write operating systems.
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You don't have the Not Affect but worried option that covers me
My Mac Pro only just made the grade for Mountain Lion, while all my other family machines should be okay for the future. However, it has me worried that 10.8 may be my last update for the Mac Pro.
I reckon you'll be OK (gut feeling), despite the whining there were valid reasons apple dropped the machines they did with ML. 64 bit only kernel ruled out a lot of kernel extension/drivers that were required for old machine hardware that the OEM probably doesn't support any more.
Apple won't be dumping 64 bit kernels any time soon.