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Stitchpunk: A subgenre of Steampunk. "Fiction influenced by the DIY and crafts element of Steampunk, with a prime example being Shane Acker's 9, in which cute Frankenstein doll-creatures stitched together from bits of burlap sack try to save the world. In a wider context, Stitchpunk emphasizes the role of weavers, tinkers, and darners in Steampunk." Termed by Acker and outlined as such officially in The Steampunk Bible (page 55). More details and examples may be found here.
Viral Marketing: Little bit. One of the most interesting ones was a random online-clip that showed Elijah Wood getting his soul sucked out while in the theater.
The Facebook account "9 Scientist" (still up, surprisingly) is the Scientist's online diary. It tells readers of the man's struggles with creating the B.R.A.I.N device, and of his misgivings with the Chancellor. Not necessary to enjoy the movie, but it furthers your appreciation and understanding.
What Could Have Been: Looking at the deleted scenes, the key around 6's neck would have been more important to the plot, with 8 playing keep away with it, and the survivors using it at the end to open a box the scientist was holding. Inside is a mirror, and a note labelled "hope" as the survivors look at their reflections.