I gotta say peeps, as a noob trying to get my head round this lot, some example pics to back up what people are trying to explain would go a long way to helping!
This is a good link, as posted by yoby earlier. Scroll down to the train pic.
Example herel
That shows the effect of firing the flash at the beginning of a long exposure. Flash takes the main pic, then while the shutter is still open but only at a dark lens aperture so only bright areas are recorded, the lights are streaked in a way that looks wrong. If you do it the other way round, so that the streeking occurs first, followed by the flash at the end, it looks better. And if the train was moving backwards, then the effect would also be reversed.
Referring to this guitar picture
http://www.gphotography.org.uk/VOiD gallery/VOiD/Solo.html
I'm not sure it is possible to say if it was taken with first or second curtain flash sync without knowing whether the guitar was being moved up or down, or perhaps whether the camera was being moved up or down. Consider the train pic again, turn it 90degs and it's exactly like the guitar moving up or down during the exposure. How can you tell if the train-guitar is moving forwards or backwards up/down?
It's a great effect nonetheless, but always an unpredictable one. And unless you know the direction of the subject's movement, I think it's better to go with first curtain flash sync, because that's your best chance of getting the timing/framing of the main flash image as it was when you pressed the shutter.
Frankly, I don't think first or second curtain synch is a very big deal. It simply makes no difference most of the time. I love slow-sync flash and use it a lot. I also use fill-flash a lot too, for different reasons. But I always use first curtain sync. Well not always, but mostly.
If you want to introduce creative bluring to slow-sync pics, then it is maybe better to move the camera rather than relying on the subject. That way you can make even a static subject appear to move, and by moving the camera, in a certain direction at a certain speed, you can get a reasonably controlled result. Using first curtain sync will increase your hit rate.
And just to reiterate, there is no difference in the amount of ghosting you get with either first or second curtain sync. Ghosting is reduced against a darker background, nothing else. You can always get a darker background by reducing the ambient exposure time, but that can also reduce the impact of the technique, in which case the only way of reducing ghosting is to position your subject against a naturally dark area of background.
Hope this helps a bit
To be honest though, I'd expect Canon are going to buck things up on the flash side anyway, they must have had some damage over the last 14 months and I'm sure they'll fight back with a better system sooner or later, it would be a little silly if they didn't.
