Unless you intend to stay in academia, the qualification probably won't pay off in terms of a higher salary vs. the years you wasted. And if you do intend to be in academia, be prepared for a long (possibly indefinite) wait before you get a permanent lecturing/research position. Post-doc life is not easy.
* 3 years wasted working on a PhD, no thesis submitted in the end, walked away back to the real world.
I think the real danger with a PhD program is that it is so easy to wander into a program, especially once you've gotten a master's degree. It feels like the right move and the next logical step, just like the previous degrees were. It's almost painless to stick around, look into interesting topics, get paid a livable salary, do some research and attend a few conferences. It can even feel like real meaningful work, without the indignity of having to find and start a job.
There is this kind of background worry that the whole thing is getting nowhere productive, or at least not at all where it's supposed to go, but it takes a few years to build up. That ends up blossoming into the regret of three years wasted, instead of a few stressful months (if that) in job limbo.
It's not all bad though. My curious distraction from my 'real work' was learning to program. I ended up with an employable skill that I enjoy using and building on. Still, though, 3 years.
Yes. Yes, yes, yes. New PhD students should have this tattooed on their arms as part of the admissions process. I wasted an entire year trying to come up with a dissertation project because I didn't understand this fact.
Ok, I will: Intellectual masturbation - It feels good at the time but is ultimately unproductive.