Recently (the day after the British plot made headlines) I flew from KCI into Midway. While the wait was reasonable in both directions (virtually no delay at all in KCI, about fifteen minutes extra coming back home), I carried on a 1.5 liter bottle of Listerine both ways without detection. At Midway a TSA even inspected my bag with gloves but either missed the mouthwash or didn't realize how easily it could have been filled with nitroglycerine. So it was hard to see the value in the extra quarter hour spent (with over 40,000 passengers per day, and using the economist's favorite tool, opportunity costs, if each of our travelers is a minimum wage earner, that fifteen minutes is costing over $50,000 in economic activity each day it is occurs--nearby O'Hare does over four times the daily traffic of Midway).
Incidentally, I didn't intentionally take the Listerine on the first flight to see if it'd be detected, risking greater delay for those unlucky enough to be behind me. I only realized it afterwards.