There is still SO much content to cover, and that's just the book content. If you add in all the new (And parts of the story that are being done more in-depth) stuff; Dol'Guldur (Necromancer/Witch King/White Council), Azog, Goblin King ... They have MORE then enough content to span 2 movies with utter ease, especially in typical Peter Jackson fashion. Extremely, extremely glad it's 3 movies.
I, like most, have absolutely no idea where they're going to end movie 2. There's alot of stuff to achieve over the 2 movies but Unexpected Journey ended at a really nice spot to kick off into movie 2. So all I can say is simply don't be worried, PJ will find a suitable place to end it and it will be suitably epic.