In case you were wondering, Time Machine does not back up a File Vault protected home directories while that File Vault user is logged in:
Whlle some may see this as a problem, I'd opt for the security that File Vault brings a mobile user over the convenience of File Vault. That's not to say that you should ignore backups. In fact, if you're using File Vault, I'd say backing up is even more critical, as one flipped bit can render your entire home directory inaccessible.
This is just something to factor into your rolling-out-Leopard plans.
