Nice tool, but I prefer to have the data already encrypted (on an encrypted block device) instead of having to encrypt the data everytime the backup runs.
Cool! If that's the case, the following part of the website should be corrected:
"While you can pipe any data into the program, the data should be uncompressed and unencrypted -- otherwise no deduplication could be performed on it."
You can use encrypted data, but only blockwise encrypted such as LUKS. Then, deduplication of ZBackup still works.
Also, this part gives a misleading security advice:
"zbackup would compress and encrypt the data itself, so there's no need to do that yourself."
Encrypting your disk is still a good idea, especially on a laptop, in case your computer is stolen. Also, a crypto block device has the advantage that encryption happens on the fly, instead of delaying the backup because all changes have to be encrypted afterwards. So the above is only advisable if you store your data unencrypted and just want to encrypt it for backup purposes.
Here's an already usable proof of concept:
http://vog.github.io/shasplit/