A small city in Hungary is shifting most of its clients and servers to GNU/Linux and saving a bundle. They still need a few copies of that other OS because people keep sending them old file formats.
“The main problem we have is with the documents we receive from the national government, companies and other institutions. They send us Microsoft Word and Excel files containing special macros, causing compatibility problems with our open source office software. So in one to two per cent of cases we have to open the documents using a Microsoft Office program.”
Clearly, FLOSS and GNU/Linux are working for them. I recommend you try it as well. see http://www.debian.org/