Complains, mostly.
One day you will call up a page on the Internet and read that Braxi bought MogaZik, and think: man, someone got rich. Wonder how that will work. Right now the sentence makes no sense, just as "Yahoo buys Tumblr" would have meant nothing in 1993. So WHAT DOES IT MEAN?
1. Nothing, if Yahoo is smart. At least nothing the users will note. They'll be on the lookout for signs that everything has been spoiled with clueless "corporate" meddling - when Tumblr itself added a small drop-down box that encouraged people to sign up, some users were ANGRY that the aesthetic was being altered on a free site that hosted anything they put up and didn't have ads.
But Yahoo will probably introduce tiny ads - you pay a billion for something, eventually you get around to wondering if it might make you some money. Perhaps they will share the revenue, like Google. Of course, commerce would spoil the purity of Tumblr. Which brings us to . . .
2. PR0N and lots of it. Either they'll let it be or roll out a slow winnow. Which will drive some people to another platform. Like MySpace! Just kidding. No one will ever go back there. It's GeoCities by now.
So far, no changes: Yahoo's CEO said the X-rated stuff can stay.
3. BuzzFeed says "The real Reason Yahoo is Buying Tumblr" is because the young demo doesn't know what it is.
Almost right. Yahoo has been making some interesting moves lately, and if wasn't for the fact that it's a legacy brand with a stupid name it might have more respect. But they have a history of buying popular sites and letting them expire from neglect, and the younger demo has seen them screw up some popular things. They're aware of Yahoo, but not in a good way.