So, Condi Rice's claim that "we didn't know" now boils down to saying that the August 6 PDB did not mention hijacked airliners being used as missiles. It just talked about the immediate near-term possibility of hijacking, or maybe something involving a building.

So, if they had clear information about imminent use of airliners as missiles, that would have justified immediate drastic action. But if it's just plain old hijacking -- well, there's no need to disturb anyone's scheduled vacation for that.

Note also the comments on this thread from Billmon, which points out that this one released text may not be the whole story; some even question whether they released the whole document...