Common spreadsheet problems; “Worst Practice”

I read an interesting article on CFO.com about the usual mistakes made when building financial models.
They suggest the following:
1) Poor Segregation of Data
2) Poor Documentation of Assumptions
3) Poor Documentation of Constraints
4) Difficulties in Making Changes
5) “Now It’s Here; Now It’s Not”
6) The Presentation Readiness Problem
They then suggest some ways to improve this:
—Encouraging the separation of [...]