As far as the accusation of Saruman that Radagast is strung out on mushrooms, supposedly the further artistic license taken by Jackson is Radagast sustains himself on mushrooms and trippy berries. Hence, as a way to explain his loony behavior.
I was semi-looking forward to Saruman's disdain for Radagast. I mean if Radagast is going to be in the film, might as well include Saruman's total lack of respect for him too, that would be nice. But if it's just going to be more recycling of Saruman's verbal backhand to Gandalf "Your love of the halflings leaf has clearly slowed your mind." Fan-tastic.
