Nintendo is clearly losing sales as a result of being unable to meet demand, hence the slip of paper as a proxy for a console in an attempt to recoup some of those losses. Every time I see someone ask a store clerk if they have them in stock (after looking at that blank space under the games), I see one more sale lost.
Predicting Wii sales to date has been pretty pointless since it's invariably the same number that they are able to crank out of the factories.
The question is at what point will stock of the Wii be regularly seen on store shelves? Once that finally happens, the "no one has it in stock so I want it" factor is gone and then it's going to be the low price factor and common favorable perception of the Wii that continues to carry sales.
Eventually it will be dependent on the strength of the games (3rd party as well) once everyone who wants one is able to buy one. Right now it really doesn't seem like games are responsible in any way for moving hardware units considering that Wii Play has consistently been one of the strongest selling titles. People obviously aren't buying consoles to play Wii Play. Did anyone hold off on buying a Wii until Mario Galaxy was released?
Odd or interesting, depending on the point of view, Wii Fit looks to be the real killer app for the Wii next year, based upon the reaction in Japan.