And once again Keith demonstrates how to condense my drivel into 6 line posts
It also brought to my attention that I left out an important bit, which is related to shutter speed while using flash. And the reason why I forgot to talk about it is...
... because shutter speed, within a given set of conditions, has no effect on flash exposure. That means you can shoot at 1/30s or 1/200s and still get the same exposure from the flash. The only exposure controls (besides flash power) that affect the flash exposure are aperture and ISO.
So what's the catch? This is only valid for the flash part of the exposure. Imagine you're in a completely dark room, and all your light will come from a flash that will fire at the moment of exposure: shoot at 1/2s or at 1/200s and you get exactly the same exposure.
Now turn on a couple of lights in the room and those will contribute to the exposure, in addition to the flash: shoot at 1/200s and you won't notice their effect (they're just too dim to register), shoot at 1/2s and you'll most probably see their effect in addition to the flash itself.
This in itself is a wonderful tool to explore, as it allows you to balance your ambient light with flash to your taste, with at least one independent control over each part:
Ambient light: shutter speed / aperture / ISO
Flash: flash power / aperture / ISO
This bit is also the reason why cameras will default to a minimum shutter speed when people turn the flash on (either built-in or add-on) in dark conditions, and it's usually 1/60s. The camera, with default settings, knows it's exposure will depend mainly on the flash pop, so it can safely ignore everything else. Everyone has probably seen those failed attempts at night time group portraits in front of a dimly lit fountain or monument, where the result you get is a bunch of people standing in the middle of a black hole without the feature behind them, right? That would be the camera using nothing but flash to light them, at said default minimum shutter speed, which is still way too short to allow the feature to be registered in the sensor. If you tried that same photo without the flash, the camera would probably tell you you'd need a much longer shutter speed to get a correct exposure for that background, so 1/60s isn't going to take you anywhere...
... cue Slow Sync flash. This will allow the camera to ignore the minimum shutter speed and use whatever it feels necessary to get the correct ambient exposure, in addition to the flash itself. Now if this exposure is too long, you might start getting blurred results, and if you're panning and tracking motion, since your flash will fire at the beginning of the exposure, you'll definitely get a funny looking streak in front of the object you're moving with. You'll get a very strong notion of motion, because of the streaks, but unfortunately on the wrong side of the object:
Imagine you're tracking and shooting a bike; what you get is a flash "frozen" image of the bike and then the streaks in front of it as it moves forward and you're panning with it. Result? A bike that looks like it's going backwards.
... cue Rear Sync flash. The camera will move the flash exposure to the end of the shutter opening time, allowing you to "freeze" the object on the right side of the image. Now as you press the shutter and pan, you get the ambient light first (creating the blurry streaks), and the flash "frozen" image right at the end of the streaks.
Whew. Right, there's still a few more points to cover (like the given set of conditions I mentioned earlier, balancing with daylight and colour), so I'll come back later for that!