My poor, overworked palm (actually a Sony Clie, but it runs PalmOS) lost its memory overnight one night last week; I think something in my pocket was hitting the power button and ran the battery dead. With Palms (and Pocket PCs), one the battery goes, everything in memory goes too, and you basically have to re-install from a backup before you can use it again. Fortunately, syncing your palm performs a backup, but it isn't 100% reliable, and it doesn't actually back up everything; when I restored the palm, it lost a few changes that I'd made late in the day before my last sync. Sony ships their Clies with a backup tool that can back up to a memory stick, but it's slow and you have to run it by hand. And everyone knows that backup that require manual intervention never really happen.
So I did a bit of searching, and found that BackupBuddyVFS is almost universally recommended for Palm backups. It's faster then Sony's backup solution, and it can run automatically at a fixed time every night.