The US Government has mandated the use of full disk encryption. The benefit of this is that if a laptop is lost or stolen, the data on it (assuming the encryption does its job) should be useless.
Full Disk encryption is probably an overkill, though. Encryption of all user data would probably be enough in most circumstances to avoid the inevitable performance (and therefore hardware-cost) penalty that encryption incurs. UPDATE: Of course, since one of the legacies of OS X’s unix heritage is that some logs and temporary files are written outside the home directory, there is a good case for whole disk encryption, on the principle that then one can be certain one has protected everything sensitive.
It will be interesting to see if they really mean it. Something has to be unencrypted for the computer to work at all - will government laptops require USB keys to boot?
We’ll see how on the ball Apple is: it’s current OS allows for easy encryption of home directories - I wonder if they’ll add encryption of the system directory also.
Some kind of tripwire system to ensure integrity has long been on my list of things I wish Apple would get around to looking at, too.