Hi,
I found this discussion very interesting as I asked the question myself.
Maybe anyone has already mentioned it, but how do you protect /tmp files or what so ever?

You need to decrypt your wallet to the .bitcoin directory, or any other place where the blockchain is.
After that you encrypt your wallet again and delete the unencrypted wallet.

Do you use an eraser tool for that? Otherwise it would not be safe enough for me;)

For me I figured out to use a truecrypt container holding my .bitcoin directory.
To backup the wallet only I use pgp and ssh (rsnapshot) to put it on a remote computer.