The issue appears when applications don't follow Apple's advice on validating App Store receipts. Copy the receipt code from a valid App Store download, including a free one, into a paid app, and if they didn't follow Apple's advice, you now have an app you can freely use.
Interestingly, the example spreading around the Web uses Angry Birds as an example. We would have expected Rovio to be a little more careful. To be clear, some are saying this works on any app, receipt checking or not, an some are saying it only works on Angry Birds.
Still others are saying Apple's instructions on receipt checking are to blamed. CraftyMind has instructions on how to fix the problem.
Even if the receipt checking hole is closed, whether by fixed instructions, or perhaps by making receipt checking a requirement for inclusion in the Mac App Store, that's just the tip of the iceberg. However, there's another threat looming, and one that's more likely to be longer lasting. Hackulous, the group that cracked iOS DRM, thus making many iOS apps piratable for those with jailbroken devices, has already cracked the Mac App Store's DRM.
The group has developed an app called Kickback that allows any app to be cracked. However, they won't release Kickback until February. As they said:
We don't want to release kickback as soon as the [Mac App] Store gets released. I have a few reasons for that.Confused? The reason for Kickback is that, just as in the App Store, there's no trial ability in the Mac App Store. Hackulous claims this is the reason behind both of their cracks, as evidenced by their wanting to have a decent amount of crap reach the Mac App Store before releasing Kickback.
Most of the applications that go on the Mac App Store [in the first instance] will be decent, they'll be pretty good. Apple isn't going to put crap on the App Store as soon as it gets released. It'll probably take months for the App Store to actually have a bunch of crappy applications and when we feel that it has a lot of crap in it, we'll probably release Kickback.
So we're not going to release Kickback until well after the store's been established, well after developers have gotten their applications up. We don't want to devalue applications and frustrate developers.
And, unlike iOS, there's no way for Apple to require Mac OS X users to only get apps through the Mac App Store. Realistically, they could, but after all this time with an open market, they would just be shooting themselves in the foot.
To be clear, there is a "Try Before You Buy" section in the iOS App Store, but that only highlights trial and lite versions, not a true trial program, as exists in the Android Market. Of course, the Android Market was recently revamped to reduce that trial and refund period from one day to 15 minutes.