Well, one of the most popular quizzes we've had turned up a real mix of answers! It seems that indeed, flash is one of the least well understood techniques.

At least here we can set you straight on one point....

The question was: When shooting with flash, which setting would you change to make the background darker?

The answer was: Shutter Speed.

Here's why. With a flash exposure, the flash duration is very short. This means that the flash has to put out all its light in a short period of time and get through whatever size aperture you have set - smaller apertures mean more power is needed from the flash, larger apertures mean less power needed from the flash. But what about shutter speed? 

Well, since the subject is being lit by the flash and that is controlled by aperture, the shutter speed is left to control how much ambient light is let in. Even with a fast shutter speed like 1/200sec, the flash duration (and therefore flash lighting the subject) is much shorter than this. For this reason, varying the shutter speed length will not affect the light on the subject (unless the shutter speed becomes long, in which case you will have more ambient light on your subject) but will affect how much ambient light is recorded in the background. 

So, to answer the question, shutter speed would be used to darken the background and you'd do it by using a faster shutter speed capturing less ambient light. This is where high speed sync flash can be useful as it allows you to use higher than the max sync speed to darken the background further.