I use truecrypt on my computers at work/home and would love to see it in Maemo.

You do not have to encrypt the whole partition. You can create an encrypted file (up to 4GB on FAT32), mount that and store important files in it. The file would be accessible to both window and linux when exported via usb. I believe that there is a "portable/thumb drive" version for windows that does not need to be installed to run.

Best of all, if you don't need to access the files, truecrypt does not need to be running (ie no battery drain).

This doesn't address all the issues, but may address enough for the average joe to use (with a gui front end) easily to protect important data.