1. An programmable logic device comprising: programmable interconnect circuitry; programmable input-output circuitry coupled to the programmable interconnect circuitry; and an array of programmable logic blocks, each logic block including a plurality of programmable logic elements coupled to the interconnect circuitry, wherein each of the programmable logic elements is programmable to implement a common set of functions, and at least one but less than all of the programmable logic elements is programmable to implement a set of supplemental functions; and wherein each programmable logic element includes at least one lookup table having input ports coupled to the programmable interconnect circuitry and programmable to implement a logic function.