| One of the open and highly debated questions in the physics of two-dimensional electron systems (2DES) is why they can behave as metals at modest electron concentration and as electric insulators when dilute. A possible reason for the failure of conventional approaches to this problem is the premise that 2DES could be concidered a "good" metal slightly perturbed by impurities and defects. On the contrary, recent nanoscale imaging experiments revealed that dilute 2DES are strongly inhomogeneous, "bad" metals, where effects of disorder are nonperturbatively strong. I will explain how such density inhomogeneities can be understood theoretically, how they manifest themselves in the thermodynamics, and what this may imply for the nature of the metal-insulator transition in 2DES. |