1. A method for diagnosing mechanical or chemical-mechanical planarization processing of microelectronic-device substrate assemblies, comprising: sensing peak drag forces between a microelectronic substrate assembly and a polishing pad along a first lateral axis; processing the sensed peak drag forces to generate a force-time relationship between the peak drag forces and time; and estimating the status of a parameter of the planarizing process by analyzing changes in the force-time relationship.