It's now on [your profile page][1].

Click your DisplayName in the header.

You'll come to a page that has the following links just left of your About Me section:

> edit | add openid | log out

Reason? Real estate in the header is premium and the "log out" link wasn't being used as much.


  [1]: http://meta.stackoverflow.com/questions/80647/why-is-logout-moved-to-my-profile-page "reason being being a reason"