I believe the shelf-life is around 10-12 years. Regardless, ACOGs are built like a tank and can take a hell of a beating (I know this from the field). The fiber optics and tritium are only used to illuminate the reticle, and the ACOG will still work even if the tritium and fiber optics lose their illumination capabilities. I wouldn't recommend an ACOG for casual use, but I also know better then to judge how a person spends their money. With that said, a person who's "mission orientation" means they'll be using their rifle day-in-day-out in situations where they need a bit more range, then sure it makes perfect sense. Otherwise, its something to think about twice IMHO.

And a battery backup for ACOGs? I guess you might be taking about the micro-dot systems that can be attached, but no ACOG model uses any type of battery. ACOGs only utilize either tritium or tritium and fiber optics.

I have an Eotech A65 on demo so I tossed it on my Colt 6940. Took that and my XCR with an Acog TA33G-H to the three gun last weekend. Results were almost identical to when I did this same thing but with an aimpoint instead of an Eotech. I was a little over a second faster with a RDS over the Acog. I would accept this time penalty and choose the Acog over a RDS becaue of the broader spectrum of capabilities. I am VERY used to RDS. What was intersting is the more I shot the ACOG the faster I was getting and closing up the gap a little bit. However, I did have 1 anomaly run where I was just blazing. It was with the Eo, I cracked off a run as accurate as the rest but just about 3 to 4 seconds faster than all the other runs. I dont really see much difference in operation between aimpoint vs eotech. My preferance is for the aimpoint by a good margin. Even though I ran it well, I just dont care for the big globby grainy ret of the Eo. The next time I go I am going to try and run the ACOG like an OEG site with a cap closed over the front and see if I can really cut down the margin between the RDS and an ACOG, my gut feeling says I can close to within less than half a second.

I run an Eotech and it fills my needs, but if your looking for something with a dot and variable power (1-4x) this doesnt look so bad, i dont know anyone who has one but its worth looking at.
http://swfa.com/Millett-1-4x24-DMS-PEPR-Combo-P42148.aspx

I ran an HWS, switched to an Aimpoint, but have the Millet DMS 1 as my backup (run it with the PEPR mount too). Pretty solid, clear glass... but it's a bit long compared to other variable power scopes, meaning it's a bit heavy (with mount, almost 2 lb). SHTF, I would probably throw it on my AR, or at least consider it strongly (pounds are pain unfortunately).