You are not alone... happened to me already TWICE with my Axim and its 1GB Sandisk SD card! First I thought it was the external card reader at fault; but the second card corruption occured when I definitely never left the card out of the PDA.
Then I found this, *very interesting* link:
http://sdprob.aximsite.com/ (it also tells you why you don't see the full 1Gb when you reformat your card)
The problem of SD card corruption is known and there is as far as I know no fix currently available.
What I did afterwards is to reformat my card using FAT32 with a COPY of the FAT table (your format app must support this)! One advantage FAT32 has over FAT16 is that it can use both the default and the copy of the FAT table. Both FAT16 and FAT32 maintain two copies of the actual file allocation table, the default and a backup copy. But the FAT16 system can use only the default copy to run your system. This means that if something happens to the FAT, your system will go down. The backup copy can be used only by low level disk utilities when repairing the default FAT. However, if something happens to the default FAT on a FAT32 system, the system will continue to run by using the backup copy until the default can be repaired.
So far this worked, I haven't had any more card corruption and my card has been on and running for a couple of weeks now.
For data recovery, if there is something important lost, I recommend you to use your card in your card reader and one of the many rescue software available for Windows (for instance Easy Recovery). In those cases like I described above, "only" the FAT table got corrupted, which means that the actual files are still intact.
I know your feeling, Bob. I was not very amused either. Speaking of Palm... I've not had a single data corruption using a Memory Stick with my old Sony Clie.
PS: for data backup I am using Sprite Backup Enterprise, which allows me to pack the files of my entire Axim including SD Card and send them via Wireless to my remote desktop workstation.