There is also a lot of value if you'd prefer to create an encrypted partition on a drive, rather than encrypting the entire disk. The problem with encrypting partitions, or encrypting certain folders using Windows EFS built into Windows XP, is that you're now relying on users to store their sensitive information properly -- users must choose to place their data on the protected partition. Unfortunately, it's poor practice to rely on the user to store data securely. People get careless, they get busy, they get distracted and they'll wind up storing data on their desktop or some other unsecure location.
Still, these are the two best options. While this mostly relates to laptops, don't forget about servers and workstations that are susceptible to physical theft, as well as thumb drives, external hard drives and other mobile storage devices.
Listen to the Storage Security FAQ audiocast here.
Go to the beginning of the Storage Security FAQ Guide.