What does it mean when my iOS app says Cleaning...?
With its new emphasis on iCloud, Apple is looking to make wireless backups of app data as efficient as possible in iOS 5 and beyond. The operating system will automatically remove temporary files stored in app directories on your device to free up space. Developers must now explicitly specify which important offline files are to remain in an app directory regardless of how much storage space is left on the device.
When an app says it's Cleaning... this means that iOS 5 is deleting unneeded app files stored in the Caches and tmp directories. This helps free up space and reduces the amount of data that will be synced when the app is synced. Although apps can't be used or modified while they are cleaning, the process should only take a few moments. After the app is cleaned the icon will return to normal.