After traveling to the USA this week, and seeing the security measures first hand, I am concerned that they remain largely ineffective, and mostly constitute window-dressing. It's as if someone said: "We have to do something." And then they did something, or anything which might help.
In my view, a sophisticated and determined attacker can easily bypass the current measures, even with the new backscatter scanners. This article in the UK's Independent newspaper suggest some serious issues with the technology, and question whether it is really fit for purpose.
A basic knowledge of the technology suggests that such systems are interested only in detecting explosive material with relatively high density. Since thin cloth (such as clothing) is transparent, then the obvious response by attackers will be to create thin layers of some suitable material, impregnate it with PETN, then stitch it into clothing. The bomber then simply needs to remove the item of clothing (for example, a turban or sari), and wrap it into a very tight bundle to increase density.
Remember, we don't need much more than 80 grams to disrupt structural integrity, according to some tests.
What about the detonator? Well, it should be recalled that many laptop batteries have been recalled by the manufacturer for their tendency to spontaneously ignite. I would think that an ingenious terrorist might find a way to rig a laptop battery to function as some form of detonator -- even while powering a laptop sufficiently to show that it works if TSA screeners become suspicious. Of course, laptops themselves have lots of places where high-density materials might be stored internally.
There isn't really an easy answer here. I suspect the TSA has many good people working on this, and are doing the best they can. However, I tend to agree with the cynical view that only two things have significantly improved airplane security in the past ten years: locks on cabin doors, and a recognition by passengers that they may well need to take matters into their own hands if a situation arises -- as one brave Dutchman did on Christmas day in the skies near Detroit.