People have also made megadollar blunders. As programming environments go, Excel carefully maximises the fuckup surface, enabling all users from novice to expert to stumble unawares into hidden calculation bugs. Cell-reference slip-ups (via copypaste or otherwise) are de rigeur, of course, and they're aided and abetted by Excel's cockeyed "type" system (if we can even call it that), half-baked documentation, inconsistent function library, and mediocre/absent testing, integrity, versioning, or debugging tools.

Probably the worst example I've seen first-hand was an entire retail banking loan-approval process running off of a single, shared, gigantic spreadsheet, that hundreds had tinkered with, but no-one understood or took responsibility for, and where the accompanying Word document of "things not to do" was bigger than the workbook.

Even yesterday, a friend of mine discovered they'd underclaimed expenses for a total >$1,000 due to a dodgy spreadsheet. Something as simple as pasting a list of dollar amounts from a webpage into Excel can produce an incorrect SUM() if/when trailing spaces creep in, since the resulting values may be treated as strings and evaluate to zero - and so it had transpired. Not even "text to columns" could fix it; you have to a) know about this lurking monster, b) use formatting to make it casually evident, and c) use Replace to strip the whitespace. What a crock.