And it now emerges that the attack may not have been imminent (the suspects had not purchased tickets and some didn't even have passports), but the timing of the arrests was forced by US officials. And this (somewhat more sensationalistic) article (via jwz) claims that the timing was "nothing more than political fabrication". And here is the Independent's roundup of what we know and don't know.
And Bruce Schneier has weighed in, on the subject of effective security and "security theatre":
None of the airplane security measures implemented because of 9/11 -- no-fly lists, secondary screening, prohibitions against pocket knives and corkscrews -- had anything to do with last week's arrests. And they wouldn't have prevented the planned attacks, had the terrorists not been arrested. A national ID card wouldn't have made a difference, either.
The new airplane security measures focus on that plot, because authorities believe they have not captured everyone involved. It's reasonable to assume that a few lone plotters, knowing their compatriots are in jail and fearing their own arrest, would try to finish the job on their own. The authorities are not being public with the details -- much of the "explosive liquid" story doesn't hang together -- but the excessive security measures seem prudent.
But only temporarily. Banning box cutters since 9/11, or taking off our shoes since Richard Reid, has not made us any safer. And a long-term prohibition against liquid carry-ons won't make us safer, either. It's not just that there are ways around the rules, it's that focusing on tactics is a losing proposition.
The goal of a terrorist is to cause terror. Last week's arrests demonstrate how real security doesn't focus on possible terrorist tactics, but on the terrorists themselves. It's a victory for intelligence and investigation, and a dramatic demonstration of how investments in these areas pay off.