Let's assume the HD is used in conjunction with a laptop that has a fingerprint scanner, like some IBM Thinkpads. What about that scenario?
That would be useful for the most part. If it were just a fingerprint scan, that would be less than optimal IMO, as they can be subverted (fairly easily from what I understand). I'm not really that familiar with the values returned by fingerprint scanners. If you could create a hash of the values, that would be a starting point to use as the basis of your crypto-key. You'd want a password too, even though users are stupid.
I'd be interested in seeing what different failure modes are like with these systems. For instance, let's say you have to replace the fingerprint scanner. Does it still return the same hash as the previous one? Suppose it is more sensitive than the previous model? Is it still the same? If not, then your data is even more vulnerable to hardware failure than it would ordinarily be.
I've used encrpted partitions from time to time. They can be useful if you understand their limitations. Do you really want to encrypt your programs and OS? On Windows, you're probably better off doing so, as your data is harder to separate from your programs in many cases than it is on Unix derivatives. If you encrypt all of the drive, do you take a performance hit? If so, is it acceptable?
There are really a lot of questions that surround such things, many of which are answerable on a case-by-case basis.