Re: ACOG issues?
I bought a couple of ACOGs about a year ago and haven't had any problems. I did hear that it was "problem" in previous years, but is a issue that was addressed. In any case, I do know guys that have older ACOGs and theirs have cracks in the plastic cover. It does not compromise anything nor does it have a negative impact on the scope's light gathering ability.
On a side note, I have to also recommend more scope for an AR in .308. That rifle has some pretty long legs and unless all you're going to be shooting is really big steel, you're gonna find yourself running out of magnification pretty quickly. I have to second the Nightforce recommendation, although I'd opt for the 2.5-10X32. It isn't much longer or heavier than the previous model, but the larger exit pupil has its advantages. If you are dead set on a low power optic, then the 2.5-10X24 might just be the ticket, if you aren't dialing it up to 10X very often.
The ACOGs are pretty mission (purpose) specific optics and really aren't very flexible, inspite of how cool they are. Quite frankly, considering the price, the glass quality isn't all that great either. The upside is that they are TOUGH.