I'll pull some numbers off Google if it helps:
116.8 million by the end of March 2008
Shows # of households from years 2003 (111.3mil) and down (93.3mil at 1990)
50 million for the US is a lock, with 60 million possible (though would require a huge, PS2-like tail). The Wii should be close to flat this year, topping over 35 million, so shouldn't have problems the rest of the way, saturated or not. No matter what its tail looks like, I believe it has sold around 25% more than the PS2 in the same period of time, it'll be hard to screw things up that badly from here on out. According to these figures(rounded NPD), the PS2 sold under 4.7mil in its 4th year due to slim shortages, the Wii will nearly double that figure.
Honestly, the Wii is doing far better than people realize. It's wiping the floor with the PS2 at a higher price point (Wii hit $200 4 months after PS2's second price cut to $180). Look below:
2002: 8.42m (15.8m) <- $100 May price cut ($200)
2003: 6.32m (22.2m) <- $20 May price cut ($180)
2004: 4.63m (26.8m) <- $30 May price cut ($150), Slim model Sept
2005: 5.44m (32.3m)
2006: 4.70m (37.1m) <- $20 April price cut ($130)
2007: 3.97m (41.1m) <- Slim 2
2008: 2.50m (43.6m) <- Slim 3
2009: 1.80m (44.4m) <- $30 April price cut ($99)
Figures are rough since there's rounding, but I threw this up anyway if it can be of use. The 2004 year surprises me, regardless of the fact it had shortage problems, imagine if the Wii had a similar drop - the reaction would be crazy. Just a great example of how this is a marathon, not a sprint. People get way too crazy over weekly sales on this site.
Aie, over 30 minutes wasted. Need to stop with this...