Workbook Horror Stories

We've all been there, I am sure, when a workbook someone else created comes to your attention (usually because you are required to work with it, but sometimes just coincidentally), and you gasp in horror at the structure of the sheets.

We are doing an audit of our Office documents before we upgrade to Office 2010. There are some crazy uses that people have put to Excel. For instance, we have several (by different people, mind you), where the user wanted to copy a range and so took a print-screen and pasted the image into a new worksheet!. We also have workbooks full of dozens and dozens of sheets where the only difference is the date at the top. This workbook is used as a blank form that employees fill out monthly. The employee is supposed to navigate to the proper sheet, print it and then fill it out. A different sheet for each month, simply to have a pre-filled date at the top.

What are your horror stories? I am sure that mine are actually pretty tame compared to some.