I came home one trip with 2 and a half cd's filled of photopass pictures....
It's DEFINITELY possible to get hundreds of photos (granted, that is also with the editing/borders while also keeping originals). However, MM includes ride photos, certain dining location photos, and all the pictures from any character greets and any spots around the park that you stop, and there'll be multiple pictures at each location.
All you have to do is utilize it! Stop whenever you see a photographer with not a huge line, ask if they can do a few magic shots, get some with just you, some with just the kids, mix it up, do some funny poses! Check different locations at different times of day, as photographers rotate, and depending on the location of the sun they might not be there yet/still.
And definitely if you're thinking of it, pre order it!