Via The Verge:

"We primarily use the Gotham font family: elegant and direct, stylish but not exclusive," Twitter explained. "Putting well-designed words in our product enhances the user experience."

I'm a huge fan of the Gotham font family (not including Gotham Rounded, which looks a bit too childish for my tastes). In fact, this very paragraph (and every paragraph here on Unapologetic) is displayed in Gotham.

There's some pushback, as with any big design change to a popular platform, but I'm a fan of this move.