Darkening a picture - the ipod/U2 silouhette effect

Does anyone know a good Photoshop technique to take an image and make it really, really dark, but still keep some definitions? Much like the way Bono looks on this TV commercial:

http://www.apple.com/uk/itunes/u2/ad/

  1. Or was it a camera effect while filming?

  2. Is it as easy as just lowering the brightness?