Love the idea, but it does precisely nothing for me at the moment.
I have significant hearing loss in one ear. The app doesn't seem to distinguish between ears(?) So when I try to calibrate it, I can hear practically the lowest noises on all the screens, so it doesn't really seem to do much whether I turn it on or off.
It's not uncommon for people to have one considerably worse ear; in fact, I would guess it's a lot more common for someone to have one bad ear (due to an infection or similar) than it is to have equal problems in both, though I may well be wrong about this, but even if still think it's worth considering. (Edit: I can't find specific figures comparing incidence of unilateral vs bilateral deafness, but there are certainly plenty of people out there in a similar position to me, e.g. see [0] and [1])
I'm actually in a privileged position of having the results of a professionally-taken hearing test, so I know exactly which frequencies my hearing is bad at too. But the app doesn't seem to show the results of the test it does, so I can't verify its accuracy.
Still, I hope it improves, because I've always wanted an app like this (or, more precisely, an app that would generate a custom corrective EQ curve for each ear). I'll watch with interest... Certainly won't be deleting it yet anyway, and it's nice to see the app itself being so polished.
Edit: I almost think the set-up screens are too simplified. If someone does have significant hearing problems, they'll be more than prepared to spend a few minutes setting it up if it results in a better correction (e.g. more frequency samples and one for each ear).
[0] http://www.hear-it.org/Single-sided-deafness
[1] http://www.singlesideddeafness.com/ssd_report.pdf