Ah, I was wondering about this as well. Does this apply also to companions? That is, is there an analogue of the companions rules from SotC in DFRPG?
Nope. I mean, both are easily adaptable into DF if you want them there, but they didn't make sense to us as we worked up the DF version of things. In the Dresdenverse it seems more right to simply have them as outright characters or as side-effects of things like aspects.
So what separates them from anything else in the Nevernever? Why is summoning a Demon something bigger than say, whipping out a fey or whatever it is Binder was calling up? Why are Demons bad news?
That's a very good question.

Are we given examples of any monsters that
haven't appeared in the books? If our players have read them all, is there anything we'll have to surprise them from the Goes Bump chapter?
Not really. Then again, building new monsters is easy, as is upgrading the pre-established models to do something unexpected.