I lost my BCN maps once as well.  Now I regularly back up the files to my laptop.  Actually, since I have well over 1Gb of map files, I usually keep them on the laptop and only transfer the files I plan on using in the near future to my Dell Axim.

REALLY late answer, but here goes. 

I use a 2-GB SD card in my PPC for my map files, plus Garmin map files, plus a few other odds and ends.  I have a USB multi-card reader for my laptop.  Before the desktop edition came out, I downloaded the maps to the card with my PPC, then I copied the files directly from the card to my laptop using the card reader.  Very fast transfer rates, MUCH MUCH faster than simply transfering the files through the PPC sync cable.  A multi-card reader that will read almost any media card costs $20-$30, or you can get a single-card reader for less than $10.

Now that I have the desktop edition, I download directly to my laptop.  I have dozens of individual map files for states ranging from California (1 map) to Mississippi (3) to South Carolina (2) to Ohio (2), totaling a few Gigabytes.  I keep them on my laptop, and only transfer the maps I need to my PPC SD card right before a trip.