All Spoilers!
The Hobbit:SoS Differences from book:
All of these changes are to facilitate adding extra material, drama, and "action" to the film.
-No significant pursuit by orcs once the Dwarves were transported to that rock (forget name) by the Eagles and on their way to Beorn's (book).
-Meeting with Beorn was a complete let down in movie. In the book it was magical. He did not try to attack the party when it first showed up (as in Movie), the meeting was cordial with charm as each member was supposed to space their arrival. I don't remember him expressing such disdain for dwarves in the book. Gandalf did not express the possibility that Beorn might kill them all.
-No Elf parties in the woods (movie)! Thorin Party was desperate in the forest running out of food, so after Bilbo peaks out of the tree tops, and sees nothing but more trees, they lose hope and end up they chasing Elvin lights in the forest only to get completely lost and caught by spiders (book).
-Bildo not caught by spiders.
-Bilbo taunts spiders with his ring on, leads them away from dwarf prisoners, then comes back and rescues them (book). Dwarves not recused by Elves from spiders.
-With Bilbo's help, Dwarves escape from Forest Elves in sealed barrels, stealth mode. Elves did not know they were in barrels (book). In movie, Elves are aware and this sets up river chase sequence. A little too spectacular for me to maintain my suspension of disbelief.
-No drama between Bard and Lake Town leader (book) that I recall.
-Exchange between Bilbo and Smaug was better in book. I believe Bilbo kept his ring on the whole time so Smaug talked to him just to get more time to figure out where he was. As in the movie, he did discover that Bilbo had some association with Lake Town by virtue of being a "Barrel Rider".
-No fighting between Dwarves and Smaug (book). In fact they were not aware that Bilbo had stolen the Arknstone and that Smaug had left the mountain on rampage to Lake Town because the jewel had been stolen. Not because Smaug was mad at Lake town for helping Bilbo (movie)? Besides, I don't believe that Smaug would leave his treasure with dwarves running all over it for any other reason that he had been stolen from and there were no dwarves about, that he could detect other than smelling a draft from the back door. Otherwise he would have stayed there and fought the dwarves (my opinion). In the book he smashed the back door trapping the dwarves inside the mountain, although at this point he left for Lake Town.