User blog comment:Rupert Giles/Global Navigation Update/@comment-24513088-20141205052251

"This experiment will have three versions of the navigation - version 1 is the new global nav exactly as we previously launched it, version 2 will have the nav scroll away with the rest of content but return as soon as the user starts to scroll back up, and version 3 will scroll away and only reappear when the user gets back to the top."

Well, I'm OK only with version 2 and 3 but I'm leaning towards 2. Also, I hope that the colours of the new bar are as customisable as the old bar at least, but I recommend you also check out what other users have to say as I can't think of anything else to say now.