Having used both all I saw on the Mac was Apple moving Spaces from the top of the screen to the side just for the sake of doing something different. Functionally they are identical.

On the iPad its messier. I can see why they did it (ie to make window management the same across devices) but it falls flat for me. Without an Expose feature 4 windows stacked up is hard to read on an 11" display. I can also only have a maximum of 4 stages on the LH-side so if I have 6-7 open at once I still have to use the up-swipe to see them all which kind of defeats the entire purpose of the stage interface.