Would everyone please pipe down about the Tumblr acquisition? Do you really think Yahoo! will just show up and start changing everything? Have you ever spent a massive amount of money on something really nice and popular with the intent to immediately change it?! That wouldn’t make any sense.
Yahoo! wants Tumblr because it is popular. If they change too much, it won’t be popular anymore. They’re not buying the product, they’re buying happy users/readers. Relax.