Depending on the application and level of security required, biometrics can have a literally fatal flaw. Let's pretend that the bad guys really want whatever's protected by the security system, and are willing to kidnap and/or kill someone to get it.
Is OS authentication more secure by
using fingerprint reader than a
(strong) password? Can that be hacked
Yes, it's pretty easy to hack off a finger from an authorized person and use that to pass the fingerprint reader. Or, the bad guys may put the person under duress and force them to put their finger on the scanner.
On the other hand, a password system can be set up with one password to give access, and another "duress" password to not only deny access, but also call for help if it's entered.
Personally, I don't work on any system that's so important that I'd want to lose a finger over it. If someone wants in badly enough, I don't even want them to be tempted to take my finger...