If I've written an article for some site, say Hubpages, and I delete it from there and it gets deindexed from Google, then reprint it on another site, would Google consider that duplicate content? Does Google "save" content anywhere to compare with, or does it do it by looking at live websites?
Yes you would be penalised by Google for copied content because a copy of content is maintained by Google for a long time even after a page is de indexed.