If you have Bitcoin-qt open or another client etc, is it possibly Linux might swap the memory (and keys) to swap? (and therefore to disk). Even though you might have wallet.dat encrypted, could the keys inadvertently be dumped to disk? How could this be avoided? Perhaps just have a lot of RAM so swapping is not needed? This could technically even occur with javascript key generators correct? Is it possible to zero-fill the swap partition after exiting the client?