The last time I traveled (NC to CA and back), I managed to get a 7" flip blade knife onto the plane. Both ways!
Now, I didn't do it on purpose, but still, I was pretty amazed. (I had given it to my GF the week before to hold in her purse, then forgot about.)
I guess the TSA agents were more concerned about all the random wires, batteries and circuit boards in my backpack, as I got pulled for bag searches both ways, yet they never noticed the knife in her purse.
Yet I still have to take off my shoes and can't carry shampoo. Its ludicrous.
A few years ago I flew back from Bend, OR to Seattle. Now the airport in Bend is a tiny little thing, the sort of place where you wait in a glass walled terminal until your plane pulls up outside and then you line up and walk out onto the tarmac and climb aboard. Security at the time was just the old fashioned metal detector you walk through and an ancient baggage xray machine, none of those fancy body scanners or anything. When I arrived back in Seattle it occurred to me that I was in the secure area of a major airport, having completely bypassed all the fancy security by taking a 40 minute flight from a small town.
One could also get a large amount of liquid or other substance on a plane by simply finding a stash point and having a few dozen people carry the allowed amount through security and deposit it in the arranged location or hand it off to somebody. It's not as if someone planning an attack wouldn't have the resources to do this.
I don't worry about it though, terrorist attacks are exceedingly rare, I'm more likely to die in a plane crash caused by mechanical failure or human error, and far more likely than that to die in my car on the way to the airport. In the US roughly 50,000 people are killed every year in car crashes, that's equivalent to a typical passenger jet going down every single day. It's so common that few even think about it, people fear terrorists but think nothing of having a few drinks and then driving home, or playing with their phone as they barrel down the highway in 4,000 lbs of steel.