I think that Skipness One Echo is missing the point. We all agree that a snooker ball in a sock is a potential weapon. But so is ALMOST EVERYTHING ELSE YOU CAN CARRY ON BOARD. The problem is that someone in a distant room actually thinks they can "solve" the problem by making lists of things not to take on board. We need to tell them that there is not enough time in the world to write down all the common objects that might be used to harm another person given enough ingenuity.
To paraphrase the IRA comment about getting lucky, whilst the bloke writing the list has to hope they have thought of everything, the terrorist only has to find ONE thing that is a useful weapon but is NOT on the list.
I suspect the security policy should concentrate on materials of use to suicide bombers, and forget about anti-personnel weapons, since as someone pointed out earlier, the current hijack philosophy makes it impossible to take over an aircraft by threatening passengers or crew in the cabin anyway, so no sensible terrorist is likely to try.