I don't see any legal battles happening against piracy, so I am also kind of worried here against buyers starting to pirate the commercial software. It could easily destroy any commercial interest.
I'm thinking about something that might help prevent the stealing in an unobtrusive manner. It would be nice for vendors to be given the option to watermark applications downloaded from the Pandora App Store, you get your own personal copy. With this I mean that any willing vendor could provide copies with some details changed that are hard to detect (and therefore remove), such that any leak or shared file that has somehow become publically available can be traced back to the original buyer. If a leak occurs, the vendor should decide what to do themselves, hopefully giving the user a chance to defend themselves and taking into account possible AppStore bugs or hacked AppStore accounts.
If this is going to be the case, I would want the app store to not do the watermarking themselves. The vendor should stay in charge of exactly what product is delivered, and watermarking will then be somewhat robust as every application could be watermarked in a different way. Also, the user ideally wouldn't know whether their software is watermarked or not (unless they start comparing two two purchases) to also give the idea that non-watermarked paid apps could be watermarked for those vendors that can't be bothered to implement this.
The code to perform the watermarking could be run by the AppStore, so that every purchase doesn't need to be stored separately for every download, and be somewhat secured such that the watermarking code or the unmarked application never leak to prevent users from being framed. Either this or the vendor must provide the watermarked downloads themselves, but then again, isn't availability of binaries the app store's responsibility?
This isn't any form of DRM, it only exists to identify the origin of each copy, and will greatly reduce the incentive to do piracy on the user part. Think of every purchase as your 'personal' copy. Currently I can't think of any reasons why this wouldn't be popular, can you?
Edit: was inappropriately replied to prior post.