I'm largely OS agnostic - I don't believe that any one system is THE one, but they each have their strengths and weaknesses.
My main personal use for windows is photographic software from Adobe, On1 and DXO. There are shareware/free alternatives, but they work differently and for my uses cannot acheive what I want with as much ease as the software I already have.
I also run a Linux box. This has been through several iterations, experimenting with Mandrake & openSUSE before settling on Sabayon for several years (rolling distributions aren't stable and I got fed up with stuff getting broken regularly) followed by Pear Linux (lovely interface, designer hired by Facebook IIRC & required to stop distro) and then Mint Mate & Cinnamon. The LB doesn't get much use these days, because having most things on a single computer is just easier in the end, when IT isn't my job.
Until last year I also ran a Mac. Good at what it does well, but a sluggish PITA that's restrictive and claustrophobic.
The thing that keeps microsoft office in dominance is compatibility. Produce a word document and you know it will look just the same in Tokyo, belgrade or New Delhi. Likewise Excel files will display correctly. OO/LO does an excellent job, but if you want to be sure your doc will be just right in front of a customer then you have to send a pdf, and there are many times that's not acceptable. Sure you can run office under Wine or use web versions, but MO is likely here to stay, and that's not at all bad unless you hate Microsoft.