The following article: http://www.smallnetbuilder.com/content/view/30039/78/1/1/
has the following statement:
"To further complicate the issue, Microsoft introduced a new version of the SMB protocol—SMB2—in Vista, which does not allow oplocks to be disabled.".

I must admit that I know NIL about the details regarding OPLOCKS, but it has always been a source of amazement to me that Microsoft persists in 'supporting' the concept given that any operational configuration can include anything from Win9x to Vista in various mixtures. I just don't see how they can feel comfortable that they've adequately tested all possible permutations and combinations.