Despite some initial reservations.
The Book: The dwarves are frustrated with their inability to make a fire in the rain. To add to their troubles, a pony bolts for no reason into the river, and Fili and Kili nearly drown trying to rescue it - but not before it lost most of the companies food supplies. Balin is the lookout, not Fili and Kili (the text explicitly states that he is "always their lookout"), and he notices a light in the distance. None of the dwarves, or Bilbo, are separated from each other. They argue about the fire, some dwarves claiming that it was too dangerous, and others arguing that it could mean some food and dry clothes. Oin and Gloin get into a fight. They decide to check out the fire, and they all creep ahead together. After getting a little closer, Thorin tells Bilbo that it's his job as the burglar to get as close as he can and make sure everything is OK. If he can't come back, he's to "hoot twice like a barn owl and once like a screech owl." Bilbo was off, before he could argue that he didn't know how to hoot like any owl.
What difference does it make? The differences here are minor. Once again, Peter Jackson plays around with the characterization of the dwarves. But like I said earlier, there's so little individual personality to them in the novel, it doesn't really matter. The changes here all lead up to the same situation: that is, Bilbo sneaks into the troll's camp by himself. It doesn't matter if the dwarves could or couldn't light a fire, or which dwarf told Bilbo to hoot like an owl.
My Opinion: For the most part, I like the changes made here. The desperation of the dwarves in finding food is an important factor in the decision to have them infiltrate the mysterious campfire. If this reasoning remained in the movie, then Thorin's decision to not go to Rivendell would be even worse - he'd essentially be risking starvation due to his own prejudices. In order to preserve Thorin's desire to avoid the elven settlement, Peter Jackson had to change the reason Bilbo needed to sneak up to the trolls. This is a good change, one that allows Peter Jackson to keep his own vision of Thorin's development without sacrificing anything important in the meantime. I also like that the dwarves' inability to make a fire was not a factor in the movie. The novel explains that "dwarves can make a fire almost anywhere out of almost anything," and that Oin and Gloin were particularly gifted at it. If they couldn't make a fire, how did the dimwitted trolls make one?