Each screener/airport seems to have their own interpretation of the rules. YMMV. People have had pies confiscated during thanksgiving '06. People have had yogurt confiscated recently. Most screeners seem more lax on enforcing the liquids rules (i accidentally had a 6 oz bottle of sunscreen go undetected last week) but if you had a family of 4 and packed a picnic lunch with yogurt and cottage cheese and possibly peanut butter in a tub or some ranch dressing see how they react.

Most of my travel is on an expense report, but I know not everyone at the airport is so lucky and staying overnight/getting rebooked on another carrier/unexpected meals can really eat into their travel budget.