The case for using Apple software of Microsoft Windows for something is so slim it tends to sound like the techno lust (sooo shiny ...) or the machinations of a mad man (I HAVE TO HAVE IE!!!!!).
Ah yes, I'm getting that XKCD 619 feeling again, where Linux advocates say about usable user interfaces, "why would anybody want that?!". I've been using and developing for Linux since 1995, so I'm not exactly a newbie. I have the latest Ubuntu on my big Linux development machine (the latest Fedora is similar in my experience) and you know the latest Ubuntu desktop with a high-end graphics card reminds me of? It's as if someone had described MacOS and Windows 7 to engineers in the old Soviet Union, and they sat down and wrote their own clunky half-a** clone based upon nothing but those descriptions. You can practically hear the clunks of heavy metal and whirring of primitive gyroscopes as you operate it. I'm sorry, but anybody who says that Linux has the usability of MacOS or Windows 7 on the desktop is drinkin' some mighty strong kool-aid.
KDE is a bloated incoherent resource-hogging mess (consider it the Windows Vista of Linux desktops), and Gnome's primitive old-school Windows 95 Meets Motif style desktop is usable compared to the competition only if you have a high-end graphics card and can enable 3D Effects and their CCCP-style Expose' and Spaces clones (I say CCCP-style because they have significant usability issues compared to the real thing). And both are limited by "X" which has significant problems dealing with the modern world and hot-pluggable monitors. As in, it doesn't do it. On the day when you can plug an external monitor into your Linux laptop and have the desktop automagically just extend onto the new monitor, with no "dead spaces" and no problems dragging and dropping things between monitors, let me know. Right now, due to Xinerama basically being abandonware, the only multiple-monitor setup that works properly is nVidia's, and only with two same-sized monitors (otherwise there are created "dead spaces" that can eat your windows so you can't get at them), and only if you manually set it up using nVidia's own setup program. Wow, how competitive with MacBooks (where it Just Works) or Windows 7 (one right-click to get Display Settings, then select "extends desktop" rather than "mirrors desktop" from the Displays options) is that? Err... not!
I use Linux where it is appropriate -- my web and email server is running Linux, and I'm developing on Linux for embedded servers that run Linux. But to say there's no reason to use anything other than Linux is just koolaid-drinking ... and, uhm, for the guy who says his HTC Evo 4G proves FOSS rocks, I might point out that the EVO 4G is running a proprietary closed-source "skin" (HTC's "Sense" UI). Yeah, that's "proof" alright... but maybe not of what the original commenter claimed :).