Ah, but what about webcams inside the fridge to show you the content? With, I presume, some sort of lighting, otherwise there's not much point?
See, killer app right there. Who has time to go opening their fridge for that sort of thing?
Seriously, though, if I could look at my phone and see the content of my fridge, that would actually be fairly useful. I can't count the number of times I've texted the Other Half from the supermarket, "do we need carrots?" (or whatever).