In the old software world, torrent sites and other piracy dens were the publisher's nemesis. But these days, few iPhone app developers spend much time thinking about piracy, even though it's very much a reality in markets worldwide.
According to Pinch Media, a mobile analytics company that has begun keeping "jailbreak detection" statistics, there are roughly 4 million jailbroken iPhone OS devices in the world (out of about 40 million, as of this past June). But only 38% of them use cracked apps—the rest use homebrewed apps built by other jailbreak enthusiasts.
The data also shows that usage of a pirated app drops off more quickly than those legitimately obtained. This may be because they're more crash-prone. Or maybe we just don't value what we don't pay for. (Below, chart courtesy of Pinch Media.)
In the U.S., the problem is comparatively non-existent beside countries like China and Russia. Check out the piracy vs. per capita GDP, and you'll see that app piracy seems to be an emerging-major-economy kind of problem; it's also common in Brazil. Should an upward trend in app pricing begin—a likelihood, as apps get more complex—it's not a leap to think that U.S. buyers might turn to the black app market.