In terms of using an open source desktop, Sun releasing OpenOffice some 15 (?) years ago was an important milestone, comparable to Mozilla finally managing to produce a working browser in Firefox. It provided essentially feature parity with Microsoft office, and most importantly, decent compatibility with Microsoft's own proprietary file formats.
I've used OpenOffice, and now LibreOffice, for lots of non-trivial tasks, including writing a complete book. Sure, the UI toolkit was stuck in the 90's, and Sun wasn't really a good steward in pushing the code base into this century, but it did work.