I think the Wii could fall 25-30% in the US this week. But others should pick up some of the slack. Maybe 10% overall drop this week.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut