The four major food groups would be: Pizza, Mountain Dew, Cheetos and Snickers bars.
Pale would be the new tan.
We'd be tuning in to the Wii Olympics right about now.
The only "Did-she-or-didn't-she?" implant debates would involve silicon, not silicone.
A-list science fair, spelling bee and chess contestants would sport corporate sponsorship patches...and have college recruiters coming to fisticuffs over them.
The Linus Torvalds Action Figure: 'Nuff said.
The bi-cameral legislature would be replaced by four Houses of Congress: Griffindor, Ravenclaw, Hufflepuff and Slytherin. Presidential candidates would chosen by the Goblet of Fire. (Bonus: Buh-bye, tiresome, polarizing primaries!)
To make social hour less of a minefield, nametags would include Myers-Briggs type assessments. The four most toxic personality aspects (e.g. narcissism, passive-aggression, etc.) would be rendered in HazMat notation.
The head of the National Academy of Sciences would be a Cabinet-level position.
Out with the electric knife at Thanksgiving, and in with the light-saber! (Bonus: Less time from oven to table, b/c the saber does some of the cooking for you.)
Rom-coms--particularly those starring Hollywood's golden children of the moment--would be automatic candidates for MST3K-ing.
The Louvre, Uffizi, and various National Galleries would add wings for anime and manga. And xkcd.
Two words: Exo-suit cagematches!
The isk (from the MMORPG Eve) would become the planet-wide currency.
Veterinarians would see a spike in cats named "Five"--thanks, @CyberCowboy!--and "Schrodinger."
All audio recordings of James Earl Jones reading The Bible would be replaced with another rendition. The Almighty should not have Darth Vader's voice--I'm just saying. ("I find your lack of faith...disturbing.")
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Shout-out to my faboo husband Dennis for his help in rounding this list out!