After nearly 10 years of using OS X as my primary OS for personal work, I switched away in late 2014. I consider it to be the best tech decision I made last year.
I started using OS X in 2005 when 10.4 (Tiger) was released. I ditched Linux at the time because I needed to print things and Linux was awful at it; OS X wasn't. I was very productive with OS X and had no serious complaints. When 10.6 (Snow Leopard) came out, I was content.
The pangs of dislike started to show up in 10.7 (Lion). The iOS-like GUI and "features" such as Launchpad didn't resonate with me. As things progressed, I became increasingly annoyed with the environment.
By the time I upgraded to 10.10 (Yosemite), my Macbook Pro no longer felt like a personal computer. Each upgrade was spent fighting the newest bells and whistles in order to keep my environment comfortable and familiar. I spent a lot of time going through the System Preferences, figuring out what I had to turn off in order to get my sanity back.
Furthermore, I found that I had stopped using the majority of the primary apps that ship with OS X: Mail, Safari, iTunes, and Apple Creativity Apps/iLife. For the most part, I ran essentially three apps: Firefox, MailMate, and iTerm2. Most of my work was done in terminals. The culture of the operating system at this point was more about sharing than personal productivity.
In short, I was working against the grain of the environment. It was a gradual transition, but OS X went from a useful tool set to get my work done to an obnoxious ecosystem of which I no longer wanted to be a part.
More damning than the lack of personal connection, though, was the complete lack of transparency and general decline in software quality, as I perceived it.
I basically got no useful information prior to system upgrades. Descriptions like "bug fixes" or "security fixes" say nothing and the links provided weren't much more illuminating. Furthermore, I had no idea as to the size of the download, so I couldn't set any reasonable expectations as to the time I was going to spend waiting.
The 10.10 upgrade was egregious. The fact that the upgrade could take multiple hours due to an incredibly slow directory merge is, simply put, the work of amateurs. Knowing about it ahead of time saved me a lot of frustration, but that kind of thing shouldn't ship. And if it does, at least don't get my hopes up by saying "1 minute remaining" for the better part of an hour.
Messages in 10.10 is a complete shitshow. It's a stunning regression. I gave up on it shortly after Yosemite was installed. The content was frequently out-of-order, mislabeled as new, and the conversation usually unparsable.
There are lots of other little things that irk me: mds being a hog, distnoted being a hog, lack of virtualization, other system services mysteriously firing up, bogging the system down. It doesn't help that the Macbook Pro I have is one of those lemons that overheats easily, thus kicking the fans into "rocket taking off" mode. At this point, my default position on Apple software in OS X has moved from "probably good" to "probably not OK". They seem more interested in pumping out quantity by way of more upgrades. It's death by a thousand cuts, but it's death nonetheless.
After reflecting on all this, I came to the realization that I was frustrated and disappointed by OS X, and I didn't see it getting better. I simply wasn't enjoying myself.
So I quit.
Once I quit, I was met with different frustrations, but they didn't feel like hopeless frustrations. I've gone back to a desktop system running Linux (for now) and while I consider it markedly inferior to OS X in terms of usability, it feels like a personal computer again. I'm enjoying the experience and I look forward to working with it, even when it's a monumental pain in the ass.
Maybe I just needed a change of scenery, but I do know that I no longer felt welcome in the OS X world, which is ultimately why I had to leave.