1. A method for placing N applications on M virtualized servers, said servers having power management capability, said method comprising the steps of: dividing a time horizon into a plurality of time windows; for each given one of said windows, computing a placement of said N applications, taking into account power cost, migration cost, and performance benefit, wherein said migration cost refers to cost to migrate from a first virtualized server to a second virtualized server for said given one of said windows; and placing said N applications onto said M virtualized servers, for each of said plurality of time windows, in accordance with said placement computed in said computing step for each of said windows.