Honestly, I am ambivalent toward it. once I got used to it shutting off at red lights, of course.
It probably saves me a MPG or two, since I tend to do a lot of in-town driving (which normally hurts MPGs).
And, for newer Jeeps, it's a great "canary in a coal mine" for when either of the batteries are about to die (start/stop is one of the first things that alarm if either the normal big battery or the smaller "motorcycle" battery cannot hold a charge.).