911 wouldn't of occured if the airport security did their job, remember that, neither would it of happened if Bush didn't ignore the threat. To be personally honest it was either a fluke or someone wanted it to happen (and I'm not just talking about the terrorists neither)
Boxcutter knives - even swiss army knives were seen as no big deal back then. It was not a fluke - they studied flaws in airport security, and I am sure did some tests - and got away with it. It was a well planned operation that went for years. They will not use that method again (unless they steal a plane without passengers) and will look for other ways to cause the most amount of deaths.
Most likely dirty bombs or nuclear devices will be used in some important area next I am assuming. Al Quada has been smashed though now, so its a lot harder for it launch operations with so many of its leaders dead, captured or on the run. Still would like to see them get Bin Laden though.