Guys as SLF I've often taken a 3-inch, lockable, serrated Swiss Army sailing knife onto about 70 sectors in the past year. I've had it taken from me by security, precisely ZERO times. However these days I don't carry it, and feel a little scared that I have no way of attacking the guy who had a knife delivered to him by possibly a sympathetic ground staffer (no offence intended to those honest people who work on the ground) - only maybe my keys poking through a clenched fist. However soon after the attacks, I thought that the dive idea had merit - remembering all the times flight attendants have been injured by aircraft encountering CAT; a hijacker on his feet will probably not be hanging onto anything & might end up with his head in the ceiling. As Horatio says, it would at least unbalance him & give the element of surprise back to the crew. These days I suspect any punters seeing anyone act suspiciously are more likely than ever to get up & grab the joker before he can do anything else; I for one would kick him into next week. I'd actually then like to gaffer-tape him to the jump seat so that he can see the successful landing, realise his life has been a failure & see the approaching police cars, before considering what might happen to him in jail...
Personally I had a get-off-and-identify-your-bag session at a European regional airport; the F/A & skipper were most apologetic. Guys & girls, please realise we SLF are behind you all the way in this - no need to apologise, we punters thank you for erring on the side of caution. No plane I'm on will be used as a weapon if I'm still standing.