I've pinched my title from a New Scientist feature which reported on research into spreadsheet errors. Professor Ray Panko at the University of Hawai'i had examined ten years of spreadsheet-error studies and found every one to show a dangerously high rate of errors. He estimated that humans make around one error per hundred spreadsheet cells.
Accountants Coopers and Lybrand found errors in 90% of the spreadsheets they looked at.
And the Computer Audit Unit of HM Customs and Excise also found errors. In only 11% of spreadsheets -- but some errors ran to millions of pounds.
The fault, of course, is with the human brain, never evolved for worlds where small errors can lie unnoticed for years, then return and bite you a millionfold. We can do nothing about that. But we can make more helpful software.