Bink.nu was just at a session on Integrity in Windows Vista from Steve Riley. "This security guy from Microsoft is always great to listen to. He talked about Bitlocker (hard drive encryption), Mandatory Integrity Checker and how IE7 behaves on Vista", mentions Bink.nu.
Also mentioned was that the goal of Bitlocker is to protect the OS, not the user's data, when your data is on the same partition as the OS your lucky. Through the bitlocker UI it is not possible to encrypt a separate data partition, with the commandline tool you can though.
http://bink.nu/Article7403.bink