We cannot speak directly for PostgreSQL's DB security features for user+password access, but we have our tech info here:
http://www.yozons.com/technology.jspIn general, all document snapshots and data stored inside of documents (as well as configuration for the system, property sets, etc.) are encrypted using 256-bit AES.  Unlike full disk encryption, this means that even if someone can hack engineer an SQL query command, they will not be able to read the data returned.  Same if they have a DB backup. 
In general, if you lose control of your server, your data is sure to follow.