TheRegister reports that the disk encryption system to be shipped with Vista, BitLocker, will make dual booting other OSs difficult - you will no longer be able to share data between the two. This encryption technology also has the effect of frustrating the exchange of data needed in a dual boot system. "You could look at BitLocker as anti-Linux because it frustrates dual boot," Schneier told El Reg. Schneier said Vista will bring forward security improvements, but cautioned that technical advances are less important than improvements in how technology is presented to users.

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Well, if I understand well, Vista won't have this activated by default. Here's how you can turn it on/off in Vista Beta. And yes it will make any data encrypted in this manner unavailable to another operating system. It does this by using TPM (Trusted Platform Module) in the BIOS and can base the key on the kernel and optionally: just the BIOS, a user supplied key, or a USB drive supplied key. This allows for the option of encrypting/decrypting data from the very start of the boot process.

BitLocker from windows is just a kernel based drive encryption software that takes advantage of TPMs just like the linux system. If you're concerned about cross platform compatibility then use user space encryption rather than kernel space encryption. If you're that concerned about secure keys then don't dual boot! If you love dual booting and don't care about encryption at all, noone is going to beat you up and make you use encryption. Correct me if I'm wrong :)