A few days ago, we investigated the new navigation drawer design present in updates to Google Earth and Google Shopper. The hope at the time was that this new Up button design would be pushed out to other Android apps. We even heard from a few Googlers that this was happening.
Now, things are officially official, as the Android Design site has updated with Matias-approved guidelines for the navigation drawer.
Things work pretty much the way we went over when we were first introduced to this. The Up button changes from a carat to a new 3 line icon when it will open the drawer.