My thought of the day is that Ruby is good to know for Chef and Puppet, the market seems high for these.
Ruby On Rails is brilliant for startups and prototyping. I hear devs talking down about Ruby On Rails, taking into example LinkedIn that has moved away from Rails to Scala and NodeJs.
The thing is, when you scale like LinkedIn, servers become more expensive than developers. In that sort of situation, it becomes a lot more interesting to move to Scala.
Scala and Ruby are both in a sweet spot, but both in a different market.
Of course there will always be the fashion of the latest skewing the market, and that can make it hard to see the effect these could have on the long term.
I also hear devs talking down about the Java market. As if Java was going to disappear anytime soon. I don't think so.
All languages suffer from programmers that have no interest to improve their skills and have a "can do" attitude.
No matter which language we are talking about, they are all bound to be spaghetti code at the end of the day. That's why there are conventions and software architects. It is like building a house, getting painters, plasterers, masons and electricians to build a house, just that there aren't any plans.
I am learning now Ruby, but I don't think I would stay there for big applications. My problem is not the language, but the lack of tools, or to be more precise, the quality of those tools. C# got Visual Studio, PHP works great with Netbeans, Java got Eclipse and Netbeans. Ruby might be good on Visual Studio, but I got a Mac.