If a BlackBerry application stores data in the persistent store, that data typically gets erased when the user performs a data transfer to a new device (using RIM's desktop software), or when the user performs an OS upgrade on the device.
I believe the RIM api does provide facilities for making an application adhere to whatever rules it needs to in order for its persisted data to be backed up and restored properly during upgrades and transfers. But the available documentation doesn't explore this very well.
What is the proper way to make your BlackBerry app behave properly during data backups and transfers?
RIM OS 4.1+