At the autoshop, where I have the car maintained and repaired, they just hose the dust off.
At the car wash, when asked for engine cleaning, they used a toothbrush and soapy water.
At my place, for the intake system, I tapped off the dust and used a microfiber duster; for the air conditioner, I soaked it in a container of water and some Simple Green for some minutes, rinsed it well, then left it to air dry before returning it to place.
How about you? How do you clean your air filter (for intake and AC)?
Peaceage