I liked the ideas of the Go-Away bomb a lot (and the name is indescribably cool). I don't think I have come across anything like it before. It seems like a very strange idea to come up with. And I really liked the explanation for how it worked. And that it is called "stuff".

And I liked the idea of dehumanising through delegation of responsibility. It is one of those things that aren't really an "idea" so much as a very apt way of putting something, so that you see it differently afterwards. Or at least I did.

I am not 100% sure what you mean by "ideas", though. As for having been done before: I think part of the point is that he is playing with things that are part of our mainstream culture. He is taking patterns and then changing them. That is the point. Pratchett does something similar, if you look at it from a purely formal point of view, but the results are very, very different.