The "logout" functionality has been effectively hidden. It is now only under the "StackExchange" drop down menu.
I would expect "logout" to be associated with my profile. If the logout link is not available in the nav bar, the first thing I try is looking at my profile. If I navigate to my user profile, the logout functionality is not apparent. The "My Logins" link there looks promising, but doesn't offer any functionally for signing out.
A drop down called "StackExchange" is pretty far down my list of places I would try to look for a logout link.
While I like many of the features of the new bar, the logout needs to be more prominent. I would suggest adding a "logout" link on your own user profile.