Apple has recently removed Airfoil Speakers Touch by Rogue Amoeba and AirFloat by The Famous Software Company from the iTunes App Store for using AirPlay APIs in a way Apple did not intend them to be used. These apps basically let you use another iOS device as an AirPlay speaker. So, for example, you could beam your audio from your iPhone to an iPod touch or iPad. Though these API's are public, it looks like some reverse engineering was needed to get them to work in this way, and that's what Apple has taken exception to. Airfoil was just taken down this week, while AirFloat was yanked last week.
Apple may just be sour that these devs have found a way to crack into AirPlay without going through the usual "Made for iPhone" accessory certification process, and allowed users to have AirPlay speaker setups without buying additional AirPlay certified audio gear.
There's obviously a big business in that kind of thing, but also a lot more quality control; there's no way of making sure these apps don't provide a sub-par experience, since there's no documented iOS API to test against. If the AirPlay is glitchy or inconsistent, then buyers might get the idea that AirPlay sucks, and will refrain from spending more on, say, an Apple TV.
There was a certain amount of noise made since these types of apps have been in the App Store for years in some cases, and have been approved over and over again during that time, including when they submitted versions with the AirPlay features.
Again, it shows that frustration doesn't only exist in Apple's curation, but in the sometimes arbitrary and sometimes delayed ways in which they enforce it.
Well, I guess the Cydia store exists for a reason... Is Apple right to shut these guys down and protect private APIs, or should they go ahead and let developers make cool apps that leverage the technology that's already there, stability and testing be damned?