I've heard mixed reviews about the Mini 30. But from what it seems is that the older, thinner barreled 30's had poor accuracy 3-5MOA but the newer ones with heavier barrels are much more accurate. Reports of 1, 1.5 and 2MOA are pretty common. This seems to be the case with most 7.62x39 semi's, the cheap, light, pencil barrels tend to flex and become inaccurate.
I think ALL 7.62x39 rifles get a bad rep for accuracy due to a large majority of weapons being built cheaply on inaccurate platforms, the cheap, poor quality ammo and inexperienced shooters who go to the caliber to plink, and can't aim. Yes, .308 has a clear ballistic advantage, due to it's velocity, but that doesn't mean that the Russian 7.62 can't shoot well.