The EVGA warranty covers overclocking, overvolting and even cooling mods and as far as I know is the only company to cover those things. They also offer the 90 day step up program where if you buy a newer card in the 90 day window they will give you the full retail price of your old card as a credit to the new one.
I have been buying EVGA cards since the 6600GT and have never had a problem with any of them.
It seems all the new Evga GTX 680's have a 3 year limited warranty. Any part number ending in AR means a limited life time warranty, their GTX 580 and GTX 570 both still carry the life time warranty also a few of their motherboards.