I have noticed two blogs picking up on what appears to be some sort of navigational data being added to the Google search results snippet. The Red Cardinal blog posted screen shots, as did Rob Hammond at his blog.
Google has confirmed this is indeed an experiment they are running, a “site navigation experiment,” they told me. Google did clarify that this data is being generated from Google and not being taken from a third-party source. Google promised to keep me posted on how this experiment progresses.
Here are screen shots from those blogs mentioned above: