As you are aware, The Hobbit is really two films - The Hobbit: An Unexpected Journey (out 12/14/2012) and the other is The Hobbit: There and Back Again (out 12/13/2013). A question that remains unknown is exactly will the break occur as the books themselves are not written with a break. Any theories are also is complicated by the fact that book was not split into separate books like the Lord of the Rings trilogy. Over at Movies.com, a TOR editor provides his own theories on where the break will occur. To me any consideration will have to factor in two things. One is it has to happen after a climactic or emotional moment and two is it has to easily lead to a climatic opening. My thinking is along the lines of the end of the Fellowship with the battle with the Orcs and the Fellowship fracturing but Two Towers opening with that awesome fight between Gandalf and Balrog. Below is summary of their very plausible theories with my opinion in italics.

1) Bilbo finding the One Ring
In the novel, Bilbo finding the ring after Gollum lost it seems like a good ending point. With the additional material being added to show Gandalf's battle against the Necromancer, it seems a natural ending point while allow more time to get to know the 13 Dwarves.
Read more »

Theories on Film Split Point for The Hobbit. There are any Theories on Film Split Point for The Hobbit in here.