These days, I primary only use irons on my target rifles, and older military guns that are more toys/range guns than anything else. M1's, M1A, 03', Mausers, Colt SP1, etc are all optics free and with their issue sights. Same goes for my Winchester lever guns, and a few other commercial bolt guns.
The advantage to the dot sights is instantly obvious when you use them, but everyone really should learn how to shoot using the iron sights.
As far as batteries going dead, or the optic failing, if you dont buy junk, its a lot less of an issue, and of course, the cowitnessed BUIS are right there if you should need them. Im still running Aimpoint M2's on most of my guns that have one, and have had them since they were the "current" sight of the type. They only have a 10000 hour battery life, and I dont even turn them off, just change the batteries once a year. Yhe newer models run much longer.
Zeitgeist - The movie
Zeitgeist - Addendum