Weird play by Amazon—they've changed their Product Advertising API so that mobile apps like Delicious Library, which pull product info from it, can't use it. Its developers were forced to pull it from the App Store.
Delicious Library developer Wil Shipley did ask for permission, but Amazon told him to yank the app or they'd shut him down themselves. So if you never got around to grabbing it, you're out of luck. And it is specifically on the mobile side that they're being prickly:
You will not, without our express prior written approval requested via this link , use any Product Advertising Content on or in connection with any site or application designed or intended for use with a mobile phone or other handheld device.
The only rational explanation—insofar as there is one here—is that they want people to use Amazon's own mobile apps to access their data and check out products, which, in a way, goes along how they're pushing Kindle as software on multiple platforms. (Software is important to them now, rather than being a dumb data provider, in other words.) I guess they think you're more likely to buy stuff from Amazon while you're poking around in their apps. [Alan Quatermain via Twitter via TechCrunch]