Foreflight on dealing with iPad data deletion.
Foreflight has published some warnings and advice for how to deal with the iPad iOS 5 behavior of deleting information unexpectedly.
If you are downloading large files and your iPad or iPhone is running low on disk space, iOS 5 can remove data from inside apps under certain conditions. For example, if you had 1GB of free space and downloaded a 3GB movie, the operating system will delete 2GB of data from other apps to make room. When this happens, your iPad home screen with display a “Cleaning” message underneath app icons that are having data removed. The next time you start those apps, they will be missing data that had been previously downloaded.
The go on to provide advice on how to minimize (eliminate?) the possibility of data being unavailable while in flight.