The pushback against Ruby/Rails has been building for a long time. There's always been jokes about Ruby being slow:
http://harmful.cat-v.org/software/ruby/
But there was a stretch from around 2005 to maybe 2008 where Rails seemed to defy criticism. It grew and grew, despite the criticism. I tried it for a project in 2006 and I became a fan. The easy use of 3rd party code, via gems, was much easier than anything I had known in Java or PHP.
I do not know a way to say when some of the criticism began to stick, but clearly things have changed. I have my own personal experience: once a fan of Ruby and now a fan of Clojure. And others have moved on -- there was recently the conversation about multi-threaded Ruby apps, and it seemed to me all the smart people agreed that jRuby is the future of Ruby: http://tonyarcieri.com/2012-the-year-rubyists-learned-to-sto...
If I had to pick one moment when some of the criticism against Rails began to take hold, even among those who had once favored Rails, it was Zed Shaw's insane rant:
http://harmful.cat-v.org/software/ruby/rails/is-a-ghetto
Even though the tone is insane, he made some points that stuck in people's heads, including mine. This was important to note:
"I believe, if I could point at one thing it’s the following statement on 2007-01-20 to me by David H. creator of Rails:
(15:11:12) DHH: before fastthread we had ~400 restarts/day
(15:11:22) DHH: now we have perhaps 10
(15:11:29) Zed S.: oh nice
(15:11:33) Zed S.: and that's still fastcgi right?
Notice how it took me a few seconds to reply. This one single statement basically means that we all got duped. The main Rails application that DHH created required restarting ~400 times/day. That’s a production application that can’t stay up for more than 4 minutes on average."
And even now, in 2013, when I have to set up a new server with Rails, even with Nginx and Unicorn and all the other systems to help me, I find Rails annoying to set up, especially compared to the simplicity of PHP running on Apache or a Clojure app bundled up with something like "lein uberjar".