Concierges, adjunct professors, potato chip tasters: US employers are relying more and more on ‘disposable’ workers

There's no way to climb a ladder without rungs. John Lund/Photodisc via Getty Images When I leave my Boston condo every day, I say good morning to the concierge, who works for a contracting company providing staff to residential buildings. When I conduct an interview in a nearby building, the people who clean that office at night are contractors. The person who serves me my lunch sandwich is a part-timer with no career prospects in that job. When my best intentions to eat well are for naught…