DTrace is used extensively in FreeBSD development these days.
It's being used to bring up new generations of Systems Programmers: http://teachbsd.org/
My team uses DTrace to develop TCP, which ensures open standards and a copyfree implementation that ends up in Apple products, Juniper, NetApp, and who knows where else. Of course, also Netflix and the large CDN I work for which run at least 1/3 of North American Internet volume.
We also use DTrace to fix the reference copyfree Intel drivers, which may in a small way pay back Illumos for the awesome tech they share. I think those end up in some popular embedded microkernels too.
I grin thinking about people that emphasize "GNU/Linux", but I will empathize with FSF for a moment to show that low level software is not particularly exciting to most. GCC and GDB are hugely influential tools for the whole open source ecosystem, especially the high growth during the 80s and 90s that led to "Enterprise" acceptance. It's hard to imagine where everyone else would be, including the BSDs and many chip companies, were it not for the GNU toolchain. Nonetheless, most people just begrudgingly use these and hope they don't give them any trouble because of course they are usually trying to do something else.
For example, at $job recently found that some of our Python code was doing 25k open64 calls but only 5k close calls during a scheduled job - this led us to find/fix a bug that would have been a disaster later.
In case others are wondering: https://en.wikipedia.org/wiki/Bryan_Cantrill
It never has really managed to catch on as a standalone tool by itself, though. Part of that's the licensing situation on Linux, but I'd hypothesize that part of it is also that it's a pretty complicated tool to use, interpret, and act on-- you don't hear a lot about SystemTap (same concept, GPLed for Linux-friendliness) these days, either.
/pattern/ { statements }
In a awk, when a line matches a the patter, the corresponding statements fire. In dtrace, when a probe matches a pattern, the corresponding statements fire. Integers, strings, arrays, and all those other sorts of features of the language are the same (though there are some special functions introduced by dtrace to help you collect and visualize aggregations).So from a language perspective, if you know awk, you mostly know dtrace. All that's left to do is learn the pattern language. If you want to do that effectively, you have to know not just the syntax of the patterns, but useful probes to listen for, and useful ways to use the information that's gleaned.
This involves knowing things about operating systems. Most software engineers don't know much about operating systems so they think the tool is stupid.
Then you haven't been looking:
http://dtrace.org/blogs/brendan/2012/08/09/10-performance-wi...
http://dtrace.org/blogs/brendan/2014/02/11/another-10-perfor...
https://www.joyent.com/blog/node-js-in-production-runtime-lo...
https://twitter.com/b0rk/status/681536144362848257
https://speakerdeck.com/sartak/dtrace-war-stories
https://www.bignerdranch.com/blog/hooked-on-dtrace-part-1/
https://medium.com/@jlouis666/erlang-dirty-scheduler-overhea...
Seriously, it wasn't that hard to find this stuff. I found the last one by searching HN: https://hn.algolia.com/?q=dtrace
Like others who replied to you, I use DTrace every day. Very often, it solves in seconds what would have taken hours without it. Frequently, it's helped solve problems I'd never have been able to understand without it. My colleagues use it all the time as well. Sometimes, I write about the general techniques (I wrote the "runtime log snooping" blog post above), and most of our bug reports in recent years are public, but we don't write about individual bugs all that often. (Seems like you wouldn't have run into them if we had, though.)
This is a technology that received an innovation award from the Wall Street Journal in 2006. Whatever impact DTrace is having today, it should have been much larger.