I use Windows but Gimp is my "go to" graphic design app. It's a solid alternative to Photoshop.

Gimp is comparatively terrible at a higher level. 3D, vector, text, smart objects, adjustment layers, ... if you are in any industry that relies on Photoshop beyond basic usage, it's very difficult to be with second string alternatives. This is just how things are in the wild, but I find it baffling that this is still the case after so many years.

It really isn't, not for professional (web) designer work at least. It might be ok for removing a couple of red eyes, but honestly the interface is so clunky it's just a PITA to use.

yeah, Gim ps is best after photoshop you should also check the browser based http://www.toolpic.com Photoshop Online Free

Windows is the reason I don't use Photoshop but, instead, use Gimp for all my needs.

Absolutely, windows is still a disaster. For developers working with open source technologies, windows is a difficult platform to use. I was attending a workshop on Angular.js and rails where I had the misfortune to have brought my windows 8.1 machine with me. Everyone, including myself, who had a windows machine could not get going with any of the workshop material.

If you develop with Rails do it on a VM, even a headless server you ssh into and export the filesystem to your Windows editor. Ruby on Windows is an inferior experience, because most of the developers in the ecosystem are on Mac and Linux. The servers are on Linux.