Price point is probably going to be the biggest factor; the original DS launched for $150 and had its first price reduction in less than a year (though that was also before one of its biggest sellers, Nintendogs, was released). The DSi currently retails for $170 and the DSi XL goes for $190. If the 3DS is $200 that could hurt its chance at sales, especially since the expanded market is one of the biggest demographics for handhelds and with the recession people are gonna be more than a little picky.

BUT, I do think the 3DS is going to be a big success in sales. With its launch lineup I have little reason to believe it WON'T be one of the biggest things that happens in the next year. I would say that a holiday launch would help it, but doing stuff in the spring would work. My estimate is probably 10 mil first year at LEAST.

18 million, given a reasonable price globally.

I agree with Aiddon : price will be decisive. 3DS is likely to retail at 200-250 USD/EUR, which will be too high for parents to buy it for their children or for themselves (especially if they already own a DS as their first handheld > gaming is not particularely important to them so they don't really have any reason to update). Therefore, 3DS must appeal to early adopters that would put > 200 USD/EUR in a new system, that is to say the core audience. Nintendo surely knows that given how they presented the whole thing at E3, but to date it's mainly re-edition of existing games. Another factor is the defiance of current DS owners disappointed by the lack of good games (these past 2 years I must have bought only 2 DS games, Ace Attorney Investigations and Fire Emblem : Shadow Dragon, which didn't receive any support from Nintendo and ended up pretty low in sales in the West), such defiance could very well prevent them from buying 3DS unless the line-up is VERY convincing.