As MEMS microphones get cheaper, it should be increasingly common to see microphone arrays in smartphones and tablets. There are already some Bluetooth headsets offering microphone arrays for noise cancellation.
I guess the large scale use of mic arrays was pioneered for aircraft detection until radar arrived, but later progressed for Cold-War espionage 'bugging'.
This is a great application for multiple processors cooperating in real-time, you could absorb as much processing power as you can buy. The trick is to achive the processing with minimal group delay, whih means processing in parallel.
Hearing aids also stand to benefit, as mic directionality is very helpful for discriminating voices in a crowd. Coupling this with assist from a camera could greatly
benefit hearing-aid users (and spooks of course).