I'm stealing this from myself, and adding some stuff. Be warned; some might sound a bit weird, but the numbers are "correct"
I'll sum it up by region.
Japan: Wii Fit has sold 2000K over 24 weeks. That's an average of 83K/week. It has only dipped below 30K once. Let's say it maintains 25K/week for the next 25 weeks. That means 625K. Then, for the christmas weeks, it will sell 600K in total. A bit on the high side maybe, but I think 1M more is a safe bet. Total for Japan: 3M
Europe/Others: According to reports, sold out, and has sold 1.25M already. It is likely to remain around 100K for the next 5 weeks at least, making 500K more, and for the next 20 weeks, it should manage 50K/week. That makes 1.5M before chrismas. Christmas could sell 1M in Europe, but 600K is a safe bet. Total: 4M
America: Preorders already at 500K +. Sales for the first 5 weeks should be 1M (excluding pre-orders) and it should easily stable at 50K/week for the rest of the year. Totalling 2.5M before chrismas. Now, chrismas times should be 1M, but 600K is again a safe bet, totalling 3M.
Notes: "Christmas times" is about 5 weeks of time, so not just the direct christmas weeks.
Total: 10M by end of 08.
Okay, non-copy and paste now.
First week america prediction:
I think people are overly optimistic. Pre-orders are at 500K, and I guess it won't sell more than 700K, as most casuals will wait to see if it works.
Prediction: 768K (one of my favourite numbers)
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS