I'm not even singling out spreadsheets - thus the link to Panko and "human errors".
But fat-finger errors are very easy to make with spreadsheets, and very hard to find. This error, (20,000 instead of 10,000) was only found when LOCOG realised they didn't have enough seats for all the tickets they'd sold.
Spreadsheets are particularly tricky because people scatter input data among all those cells; Sometimes data is manually copied and pasted (which can either update automatically with outher changes, or not, depending how it's cut and pasted); they then manipulate those cells with formulas (sometimes across multiple sheets) and then they spit out a number. Or sometimes not even a number but a bar on a chart. Few people bother looking at the input or at the formulas used, they just see the output and sometimes apply a brief sanity check.
> You could argue that there should have been error handling or data validation, but most custom software doesn't do that either.
Most people don't write custom software. Spreadsheets give people a very powerful tool. Most people don't have the skills to protect themselves from that power - they don't know about error handling or data validation and spreadsheets make it hard to provide those sanitation and checking tools.
When I read that Eusprig literature on spreadsheet errors a few years ago, it seemed to me of rather low quality. Certainly many spreadsheets contain errors, but what are we comparing this to? Software in general contains errors. Custom app software—the only alternative to spreadsheets in most cases—tends to be of poor quality and is very expensive compared to spreadsheets. So it's far from clear that spreadsheets are a bad tradeoff.
Programmers take it for granted that "proper" software is better than spreadsheets, but I think that is mostly bias. Intellectually and technically, spreadsheets are low-status. Among users, on the other hand, they're high-status, for very good and deep reasons.
I'm also biased. I think that these problems need to be solved by innovation within the spreadsheet space itself.
But people are bad with numbers and spreadsheets give them the power to be bad with lots of numbers very quickly.
Spreadsheets are tricky to audit, and often they're not audited because they're just a tool that some guy uses without anyone knowing.
I've mention the EU SPreadsheet Risk Interest Group before, but here's the link for people who haven't seen it (http://www.eusprig.org/)
Panko has a nice website with some information about human error and the things that people do with spreadsheets (http://panko.shidler.hawaii.edu/SSR/Mypapers/whatknow.htm)
If you like Excel and pivot tables you might like PowerPivot, a free addon from MS. Here's some information about it: (http://www.powerpivotpro.com/what-is-powerpivot/)
EDIT: I like some of the horror stories here (http://www.eusprig.org/horror-stories.htm), eg
> The London 2012 organising committee (Locog) confirmed on Wednesday that a decidedly unsynchronised error in its ticketing process had led to four synchronised swimming sessions being oversold by 10,000 tickets.
[...]
> Locog said the error occurred in the summer, between the first and second round of ticket sales, when a member of staff made a single keystroke mistake and entered ‘20,000’ into a spreadsheet rather than the correct figure of 10,000 remaining tickets. The error was discovered when Locog reconciled the number of tickets sold against the final layouts and seating configurations for venues, and began contacting ticket holders before Christmas.