I have been playing in CS5 Extended and have done some work with the stacked layers feature. Essentially it allows you to stack your photos one on top of the other and have non-common elements of the photos show through each layer. You then have multiple ways you can have the photos add to one another, one of which is to multiply them on top of each other. This method works brilliantly for fireworks and I am pretty happy with how the photos from Canada Day 2011 came out using this feature.
