Why do people set themselves up for disappointment by hyping a game's potential sales numbers to levels they can't possibly reach? For example, looking at the number of games that have actually reached 12+ million LTD worldwide, it seems unreasonable to predict that for Brawl after 1 day sales figures in one territory.
I think people are over-predicting the legs of this game. It won't fizzle as fast as most Rpgs do, but the Smash Bros series is now an extremely anticipated series. SSBM was more front loaded than the first Smash Bros, and I think this game will be even more front-loaded than Melee. That said, Wii is doing better than Gamecube, so I think overall LTD sales of Brawl will be up compared to Melee. Say 600k+ first week and 1.8-2M LTD.
Worldwide, I think brawl will be in the 8M-10M range, based on how much better Nintendo's other main franchises have been doing on Wii (Twilight Princess, Mario Galaxy). SSBM hit ~6M World Wide for comparison.