Should Nintendo worry?
Short answer; yes
however, they also have a lot to gain from the move.
Sony and 3rd party development relations will absolutely create more multiplats for the wii, and these games will be of greater quality than most 3rd party wii games imo.
Now two consoles use motion in the same way, (with Natal being somewhat different) and developers that previously supported hd consoles will turn their efforts towards motion controlled games on the PS3 wii.
But Nintendo is no longer alone, and they will need to pay close attention to how the perception of the wii/ ps3 change with the introduction of Sony's move.








