Robin Good: Here's a great visualization of how different can be the traits of content re-use. In the left column you can see what would appear to be the ideal traits of a professional curator, while on the right you can immediately recognize the ones of scrapers, republishers, cheap aggregators and other "thin" publishers as Google would call them.
I think it can serve as an excellent reference, when in doubt about whether you are still doing the right thing or not, when it comes to re-using and republishing other people content.
The table is part of an excellent presentation entitled "Link Building by Imitation" and authored by link building expert Ross Hudgens.
Via Robin Good, Marc Lucas