Ruby is also slower than C++ & Go, But Ruby on Rails is not only popular but a very productive web framework which can help you build your app with a productivity that C++ or Go can't match.
When you write a high quality, fault tolerate system, the raw speed comes at the end. Erlang shines when you write a concurrent system plus its design is very unique. Erlang I would say isn't only a language but a whole philosophy of Software development. Once learned you can apply to many other platforms.
All in its a joy to work with functional languages and Erlang is perhaps the most commercially successful functional language.
This is similar to the ADA argument -- it's great and can be used to write safe software, but do you need safe software a month from now or unsafe a week from now? Global networks with millions of users are extreme outliers.
- A large system never runs on a single machine if you want any level of realistic fault tolerance. Two nodes is a bare minimum, 3 an acceptable one.
- The number of nodes will always depend on where your bottlenecks lie. Erlang developers would be rare and few to write CPU-bottlenecked code directly in Erlang. The usual approach would be to write your system in whatever is appropriate, and then too coordinate things with an Erlang layer.
- I would a hundred times more willingly maintain and debug a running Erlang system than a C++ one. I'm kind of sold on the idea though, and wrote http://erlang-in-anger.com to share my experience there.
Out of interest, what makes you say that?
Looking at the TIOBE rankings (not that this is definitive), Erlang doesn't even make the top 20 languages, when F# and R do:
Is there a reason you think it's more successful in the commercial world?
(btw, I'm a fan of Erlang - unfortunately I don't get to use it on a regular basis; other than products built on it: RabbitMQ mainly)
Just to mention one, RiakDB, a successful distributed software system is developed on top of Erlang. Actually I've yet to see any other product used by 100s or perhaps 1000s of developers developed on F# or Haskell. Not to mention, almost over 80% of telecom industry is running on Erlang.
Rabbitmq -- probably the most popular messaging system
Riak -- distributed, fault tolerant database
WhatsApp -- managed to route billions of messages a day with only a handful of engineers and servers.
Ericsson -- pretty much got the market for cell base nodes cornered. Chances are about 50% if you use internet on your smartphone, that Erlang will be involved.
Some firms on Wall Street use Erlang -- remember Serge Aleynikov case, he is an Erlang programmer.
Ejabberd -- a very popular XMPP server
CouchDB/Cloudant(IBM) -- another database and database-as-a-service company use Erlang.
So I would still say the original statement holds. By success might mean the amount of work being done not amount of people writing code. Think about WhatsApp. It was only 10-20 engineers that worked on the back-end yet think about the massive amounts of data they were able to handle.
His erlexec thing is quite useful: https://github.com/saleyn/erlexec - I started contributing to it myself before I realized who he was.