I use primarily open-source apps, but I still use Windows because I think Linux is way too far behind to be reasonably cost-effective for personal use. This is a pretty good summary of my gripes against Linux, and also against open-source development in general.

I’ll add that this is one of my primary problems:
2.1 No good stable standardized API for developing GUI applications (like Win32 API). Both GTK and Qt are very unstable and often break backwards compatibility.

This is how open-source developers’ poor understanding of UI design and user experience are embedded into Linux design. To get a taste of this, install GIMP on Mac or Windows, and notice how the dialog boxes (particularly the open/save dialogs) are different from what you’re used to. In fact, GIMP open/save dialogs are vastly inferior to Windows WIN32 API open/save dialogs. I’m not willing to take such a major hit in usability just to save $100 on my operating system.