The Book: After climbing down from the tree, Bilbo relates what he saw to the rest of the dwarves. They grumble at him, especially at his report of wind and sun, and bemoan the fact that the forest seems to go on and on. Hunger pains them, and Bombur refuses to go any further. Balin notices a twinkle of light in the distance - a campfire. Too hungry to care about heeding Gandalf's warnings to stay on the path, Thorin's Company rush toward the fire. It's an elven feast.
"Elves. Why did it have to be elves?"
As soon as the dwarves approach, the torches and campfire wink out like magic. The dwarves panic in the lightless dark and it is many hours before they can find each other again. By then, they are hopelessly lost. They make camp, and shortly afterwards Dori sees the lights in the distance again. Bilbo is sent to scout. As soon as he steps into the clearing where the elves are feasting, the lights wink out and he immediately falls asleep. It is only by accident that the dwarves find him. A third time the dwarves notice the lights, and a third time they approach - this time they witness the elven king himself. Thorin approaches the campfire, instead of Bilbo. As the enchantment causes Thorin to fall asleep, the lights disappear again, and Thorin's Company is separated for a third time. Bilbo wanders the forest calling for his companions, but does not find them, and he is forced to make camp by himself. He is woken up by a spider, who is halfway through spinning him into a web cocoon.
My Opinion: I'm of two minds about this change. I certainly don't think that I would have wanted to see Thorin's Company crash three elven parties in a row; that'd get very old, very fast. But we could have seen one, right? I know that there isn't much time in this two and a half hour movie, what with all the Legolas drama and exciting barrel chases, but, c'mon. This isn't an adapted scene that failed to live up to what the book delivered. It was cut entirely! Another interesting part of Bilbo's quest just entirely removed. And it involved elves! That's, like, Peter Jackson's favorite thing, right?
You could have used this guy if you wanted to. He's got orange hair! I know how much you like orange!
A smaller note, but still a change that bothered me: this is the second time that hunger has been a driving force in the dwarves' actions in the book, and both times the movie ignored that particular motivation. When Thorin's Company risked the trolls for food, it was because their ponies bolted with all their provisions. This time, though, they're out of food because they've been in Mirkwood for so long. Removing this small subplot isn't a big deal in the long run, but it sort of changes the scope of what's happening. Again, the movie just feels so rushed, like Bilbo and the dwarves are being hustled from one scene to another. Bilbo's grand adventure is supposed to take months! Not days.