Where have you folks been all this time? One of the first things I blogged was a note on the lack of followup on the Moussaoui arrest, and when the indictment was announced, I made a note of the less than forthcoming answers which Mueller and Ashcroft gave in response to the obvious questions.
The real question is, if the White House now admits to a nonspecific warning about al-Qaeda hijackings, might they still be covering something up? One possibility comes from a report in the generally reputable Frankfurter Allgemeine Zeitung (via the Washington Post) hinting at specific warnings about the use of commercial aircraft as weapons --- on September 13th.
(via Atrios, who is generally all over this; his taxonomy of tinfoil hats is particularly useful; he also has an amazing amount to say about what Ashcroft did do in response to the warnings in August; he stopped flying commercial).