Seems like this topic has been brought up as people want to compare the Switch to various previous launches. Thoguht I'd comb around and see what other data I could find. Kinda fun to peek back at past systems, here's what I have for first month sales in the US:

PS4 - 1138k (Nov. 15, 2013)

XBox One - 909k (Nov. 22, 2013)

Game Boy Advance - 880,784 (June 11, 2001)

XBox Original - 722,177 (Nov. 15, 2001)

GameCube - 662,560 (Nov. 18, 2001)

Sony PSP - 620,000 (Mar. 24 2005) *source on this is iffy

Playstation 2 - 500,000 in first weekend (Oct. 26, 2000)

Sega Dreamcast - 514,000 in first 2 weeks (Sept. 9, 1999)

Nintendo DS - 479,000 (Nov 21, 2004)

Wii - 475,000 (Nov 19, 2006)

Wii U - 425,000 (Nov 18, 2012)

Nintendo 3DS - Just Under 400k; 440k in 1 week  (Mar. 27, 2011)

Nintendo 64 - 326,000 in 2 days (Sept. 29th, 1996)

XBox 360 - 326,000 (Nov. 22, 2005)

Playstation 3 - 187,000 (Nov. 17, 2006)

Bonus data: For September 1996 (two days worth of sales) the two N64 launch titles sold as follows: Super Mario 64 (282,000) for no.1 on the month and Pilotwings 64 sold 85,000, good for no.4 that month. 

Looking back on it, GBA, GCN, and the original XBox had really good launches. Nintendo has definitely been undershipping launch hardware since the GameCube. 

PS4 and XBox One launches were ridiculous. If anyone has launch sales for Playstation 1 or SNES that'd be great. I think the Console Wars book has some data for the SNES early days, I'll have to look over it again. 

It would be interesting to see an aditional figure with "launch aligned" for consoles with different launch dates in different regions

Dreamcast launch was really good too, I don't remember it being so high. That would've been the best launch in hardware history in the US until that point I think. That system really sank like a rock after launch unfortunately. 

That ps4 record is not gonna be broken anytime soon

Probably not. PS5 or XBox Next would be the only ones with a shot. The Xbox One number is almost more impressive considering it was $100 more. 900k+ is insane for a $500 system. 

At the time, it was called the biggest single day for entertainment revenue, ever--or something like that. Bigger than any movie launch, sporting event, concert, or anything.

Thinking back, it's funny how they twisted the PR. But, it was technically true.

Yep, here it is:

http://money.cnn.com/1999/09/09/technology/dreamcast/

"Sega fires the first shot Thursday in the battle of the next-generation console systems, as its 128-bit Dreamcast machines go on sale in the United States. The company anticipates generating nearly $45 million in sales in the first 24 hours, which it says will be the biggest moneymaker in the history of the entertainment industry, surpassing the first-day figures set by the summer's biggest blockbuster movie: "Star Wars Episode I: The Phantom Menace."

I really have fond memories of the Dreamcast, pity it bombed. I remember working at a Toys R' Us and trying to suggest it to people that Christmas, but they were dead set on waiting for Playstation 2. 

Most interested in how it compares with the Wii, Wii U and 3DS

Hmm, didn't realize the original Xbox had such a strong launch. Goes to show how little the first month matters, even the Wii U had a good start globally. Pre-orders and first month sales as markers for future success are as useless as holiday numbers for deciding June, July and August baselines.

well, GC and GBA > wii first week on US...
So, that statment doesnt make sense:
"2. Fri-Sat sales for Nintendo Switch exceeded first 2-day sales in Americas for any system in Nintendo history. Next biggest was Wii."

EDIT: well, i realize that it is described for whole month. Now im confused, everything is possible. How many units can we expect for these 2 days?