I'm considering using FileVault 2 when I upgrade to Lion. Though my understanding of it is weak, it seems as though it shouldn't really increase the number of reads or writes per disk operation compared to a non-encrypted drive.
I don't even know if there's any kind of encryption that would increase reads/writes dramatically, since all decryption presumably happens in memory. But it seemed like something I ought to ask about.
Is there anything I'm not aware of here that I should be?