It was nice of this stone cold badass to let Kili fire off an arrow before fucking that warg's day up. It's important to let Little Beardless feel important every now and then.
Thorin realizes that an orc pack is nearby, and Gandalf declares that they are being hunted. Ori brings even worse news: the ponies have bolted. Radagast offers to draw them off, but Gandalf warns him that the Gundabad Wargs will outrun him. "These are Rhosgobel rabbits!" says Radagast. "I'd like to see them try."
The Book: No such scene occurs. There is no indication that Radagast was involved in the investigation at Dol Guldur. Thorin's Company is not attacked by wargs at this time, and they had their ponies until they were all captured by the Goblin King. This scene is entirely an invention of the movie.
What does it matter? I'd like to keep my discussion about the investigation of the Necromancer and Dol Guldur in another post, but one very important thing here is worth mentioning: Gandalf's insistence that Dol Guldur is abandoned. In the book, he knows it isn't - in fact, it's where he found Thorin's father, half dead, tortured by the forces of the Necromancer. The depth of this change is actually quite significant, but like I said, it's a topic for another post. I just wanted to draw attention to it here before discussing it again. Radagast plays a very large role in things, now - both by being the catalyst that draws Gandalf's attention to the Necromancer, and by saving the dwarves from the orc attack. His presence causes changes that further distances the plot of the movie from the plot of the book.
My Opinion: We know Gandalf's worth. And as shitty a character as Radagast is, we know he's a capable fighter. Many of the dwarves are warriors. Why, then, are they running from an orc pack, when they have two wizards with them? It's ridiculous. It's bad enough that the scene has nothing to do with the source material, but it's so incredibly contrived that it honestly drew me out of the story. Why retreat? Why not stay and fight?
Radagast, once again, proves to be a humiliating disappointment. His entrance into the scene is marked by shouting random bad things (thieves? fire? Are you warning people, or just screaming about shit you dislike?), then he just continues to act goofy and stupid. I don't know what was up with that bug in his mouth. A random, Family Guy-esque non-sequitur joke? Or is it supposed to be funny that he actually transports insects in his mouth? His battle with the Witch King was pretty cool, but any hopes I had for the character were dashed when I saw him take a hit of Gandalf's Old Toby.
Yeah, we get it, he just got high. Were the cartoon tweety bird sound effects really necessary?
As much as I hate Radagast, though, I really do like the decision to have him involved in the investigation of Dol Guldur. He does live closer to it than anyone else, and it absolutely makes sense to have him notice the darkness in Mirkwood (née Greenwood). This is an excellent decision on Peter Jackson's part, one that fits the role of the overarching storyline, as well as the purpose of the wizards. If only Radagast wasn't such a fucking joke, I'd give it my full support.