Knowing that the "3-oz rule" doesn't apply to checked baggage, it was safe for you to assume that I was referring to the TSA's screening of carry-on luggage. At MSP, the rule is clearly posted and 1-qt bags are provided for travelers who aren't prepared. I'm not sure why things are so different at SFO.
Here is the TSA's explanation of that rule:
http://www.tsa.gov/311/index.shtmBoarding passes and identification are required of adults at security checkpoints, which are manned by the TSA.
Again, the TSA explanation:
http://www.tsa.gov/assets/pdf/summer_tips.pdfAnd except for this one time at SFO, I've always had to show ID while checking luggage. Usually it's the airline employees who accept the luggage from passengers. Sometimes the airlines make the passengers haul their (checked) luggage directly to the TSA screeners.
As for the color-coded Threat Level, it supposedly reflects the amount of diligence with which security agents inspect passengers, cargo, luggage and so on. Hearing the Threat Level might make "soccer moms" feel safer, but announcing it is counterproductive insofar as it lets anyone who's up to no good know how thorough the screening and surveillance is likely to be. Israel knows a little something about security and I hear that they don't tip off anyone by announcing how closely they're watching at the airport.
I agree that most of it is "Security Theater" - a term coined by Bruce Schneier. Except for securing cockpit doors, most of the "security" measures implemented since 9/11 are a waste of time.