One of the more significant new features included in Apple's iOS 5 release is iCloud. iCloud is your "hard drive in the sky" that keeps your devices in sync, and also serves as a backup mechanism. Each user is given 5GB of free storage, with additional storage available for purchase.
As part of the iCloud rollout, Apple has issued new storage guidelines for developers. These guidelines state that only user-generated data should be stored in the <Application_Home>/Documents folder. This data is automatically backed up to iCloud and goes against the 5GB cap. If an app stores too much data in this folder (as deemed by Apple), then it can be rejected from the App Store.
The Webtrends iOS Mobile SDK had been storing event data in Documents folder. In our latest release (126.96.36.1990) we changed over to use <Application_Home>/Library/Caches folder instead. If any event data exists in the Documents folder during an app upgrade, the SDK will automatically move it to the Library/Caches folder as well. We recommend that you update your apps to use the latest release of the SDK as soon as possible.
iOS Data Storage Guidelines (login required)
iOS Developer Library - File System Basics