What’s the result of Github/Stackoverflow changing the top navbar?

Github, and StackOverflow change the top navbar a quite a while ago. As I remember, some people really hated this as it initially came out (at least in China).

For myself, now I'm really get used to it. But I'm wondering the opinions of others, and wondering if there is any data supporting the changing decision. And this remind me of people's reaction when the iOS change its design into flat style.

I feel like this question is a little bit too broad, so I'll give some specific questions:

  • Is this change necessary? Any improvement on any kind metrics?
  • When making UX/Design decision, how does the designer withstand so much opposition at the initial changing stage? Is there any other good examples?
  • Given the time it takes for people to get used to the flat design and other stuff, is it possible to really test the reaction before launching it?

Some related links: