A lot of people use Spreadsheet::WriteExcel I think. At least I get a lot of emails related to it. At the same time I don't generally get an insight into what people use the module for. There are some obvious tasks that I can imagine such as invoices or inventories or balance sheets and the email addresses of the correspondents suggest a heavy usage among financial companies. The occasional example Excel file that I receive isn't usually very exciting, not least of all when viewed in a hex editor. As such Spreadsheet::WriteExcel is used for the mundane reporting we all have to do occasionally. (Apart from me that is. In the eight years with my current company I've only used Spreadsheet::WriteExcel once and that was in the last six months. So much for eating your own dogfood).
That's why I was blown away when Rick Lavigne contacted me to say he was using Spreadsheet::WriteExcel to produce Tulip Diagram roll charts for motorcycle navigation. If you don't know what that is, and I certainly didn't, have a look at Rick's website rollcharts.org where it is all explained in detail. In particular the quality of the finished worksheets really impressed me.
In fact it impressed me so much that I felt obliged to help Rick out. He had written to ask if a document properties feature was planned. It was on the TODO list but with a low priority so I moved it up the list and implemented it. There probably aren't many advantages to running your own Open Source project but at least you can set your own priorities.