Filevault is too much of a good thing but slowing down your system and making Time Machine backups difficult if not impossible. No security is also no option, so I thought about creating a sparse image for just a few selected datasets, like mail, calendar, passwords and adressbook. Why should I encrypt 120 Gig when only 8 Gig should be encrypted? The sparsebundle is mounting automatically using a password from the keychain.
I found it, however, difficult to create the correct links that replace the original files.
A Mac OS X hint fortunately explains, how to do that (~/Documents/PRIVATE/ is the open sparse bundle), making Knox superfluous.

# adressbook
$ cp -Rv ~/Library/Application\ Support/AddressBook ~/Documents/PRIVATE/
$ rm -Rv ~/Library/Application\ Support/AddressBook
$ ln -sv ~/Documents/PRIVATE/AddressBook ~/Library/Application\ Support/
# calendar
$ cp -Rv ~/Library/Calendars ~/Documents/PRIVATE/
$ rm -Rv ~/Library/Calendars
$ ln -sv ~/Documents/PRIVATE/Calendars ~/Library/