Much has been made of the fact that the terror alert was based upon old data. On one hand, there seems to be a valid concern - if the administration is sitting on old data until an arbitrary point, questions of its competence and motivations do arise. On the other hand, just because the data is old does not mean that is bad. Case in point - the World Trade Center was not attacked once - but twice. 2001 was the second attack, 1993 was the first. Data that was "old" in 2000 about the WTC being a desirable target may have been especially helpful on September 10th.
The big question is not whether the data was "old" but why it is being acted upon now. Maybe new information came up. Maybe new analysis was done that gave it heightened signficance. Or maybe the administration is cynically manipulating the terror alert system to great a climate fear so as to induce a Republican vote. You'll find people who'll agree to anyone of those explanations, but most likely the one they choose to believe will be determined by their partisan politics.
Personally, I think the first is true - that new data arose. While there is the "climate of fear" does affect peoples choices, you'll be hard pressed to argue that the danger is not real. The fact is that explosives and other weapons are all to easy to make, conceal, and use. And there are many out there who have their reasons for wanting to take advantage of their destructive power.