AlyssaS - 2:07 am on May 1, 2011 (gmt 0)
I would add "pages with duplicate subject matter" as a subset of 6. "too many useless pages".
For instance ehow has pages and pages on how to boil an egg. Each has a very slightly different title - so "how to boil the perfect hard-boiled egg", "how to boil the perfect soft-boiled egg", "how to hard boil an egg", "how to boil an egg in a microwave".
They all have slightly different titles, and the text is worded differently so they pass copyscape, and are supposedly "unique" - but arguably they are about the same thing and could all be condensed into a single 1500 word page with sub-titles for hard-boiled, soft-boiled, microwave-boiled and so on.
I think if you have too many of these over-lap subject matter pages, you get flagged, as this is not the natural way to explore a subject.
It costs G time and money to index these pages, and when every site is producing 15 pages on something that warrants a single page, it adds up to a lot of garbage.