According to the Empire Online interview with PJ and GDT (link above), the two movies will include all of the iconic moments in the book, The Hobbit, as well as being expanded to follow other events that occur ‘offstage.’ This includes the White Council and Gandalf’s comings and goings to Dol Guldur.  Pj: “We expanded out the universe a lot more so that we weren’t just staying with Bilbo and the Dwarves on their journey, as the book pretty much does. We started to expand some of what’s happening to Gandalf outside of that journey.” Things we know are included so far:

– backstory of Thrain, Thorin’s father

– Beorn

– Spiders

– The White Council

– Gandalf’s journeys to Dol Guldur

– The three trolls (Tom, Bert, William)

– Sauron ( including some of his history)

Useful Links:
Message board thread: What does a “sequel” mean?
GDT comment about the 2nd Film
(Also see Empire Magazine link in 1.1 above)

In a nutshell: no. In the early stages of their collaboration, PJ and GDT planned to film the events in the book The Hobbit as a stand-alone movie, with a second movie, or ‘bridge move’ as it became known, used to address events outside of the primary storyline of The Hobbit, continuing to where the Lord of the Rings movies pick up the story again. Fairly early on, however, they confirmed that it made much more sense to film the storyline of The Hobbit over the span of two films, addressing events outside the story at the same time. ill span both films. PJ: “We just decided it would be a mistake to cram everything into one movie.”