according to the answer here:
http://bitcoin.stackexchange.com/questions/19834/multibit-security-with-regards-to-backup-foldersMultiBit deletes the unencrypted wallet files stored on the 'wallet-unenc-backup' folder (once you set-up a password, of course) and replaces them with an encrypted copy, which means the unencrypted wallets are NOT there :
The password used is the one you use to first encrypt your wallet. MultiBit goes through all the unencrypted wallets, creates an encrypted copy and secure deletes the unencrypted one
So, are there any other wallet/private key files that ARE NOT encrypted in multi bit folders ??