Perhaps the biggest improvement on the Due over the previous models of the Arduino is the switch from the traditional 16MHz 8-Bit processor to the Atmel SAM3X8E, a 32-Bit ARM Cortex-M3 clocked at 84MHz. This is a quantum leap in processing power, making it possible to sample data from connected sensors thousands of times faster than on the older models.
The Due also greatly expands the interfacing capabilities by increasing the amount of I/O pins and adding 12-Bit analog DAC. With this new hardware, it will be possible to do things like directly drive speakers for audio playback. In addition, the Due now includes two USB female micro-USB ports; one is for the traditional programming functions, and the other can be used for USB host or client mode.