Its not a silver bullet, but it is specifically designed for problems like Twitter's back-end issues. If it can handle running telephone systems for years at a time with a large string of 9s of uptime, I think it can handle broadcasting SMS. Well. Its the most proven tool for this type of job and the only one I'm aware of designed from the ground up for building applications like twitter that are utterly reliable.
Not a case of magic, just the right tool for the right job. You could code a web app in C, but why would you? Making twitter in Ruby (and to a lesser extent Scala) is the same thing.
I clicked the profile link to your blog, and it looks like you have a lot of Ruby experience. Compare the syntax for message passing between Erlang and Ruby.
id ! {my_fun,Args},
Thats it. Passing messages between pids on nodes across a network isn't much harder.
Compare the difficulty of parallel computation and storing data in parallel across many systems reliably between Erlang and Ruby. Doing that stuff in Erlang is just as easy as doing CRUD in RAILS, because the tools are designed to make it easy.
The downside is that Erlang is pretty bizarre and hard to learn if you've never coded in a functional language - you only get to set values ONCE, etc. Thats a critical feature for debugging large pools of processes working together, but it sure is strange. Which is why you wouldn't use Erlang to do a simple CRUD web app, you'd use RAILS.
Seriously... its an entire language based around passing messages between lightweight pids working in congress, across many systems, with built-in fail-safes for any failures, and a rock-solid distributed/redundant data store baked in.
In this situation its just about as close to a silver bullet as you will ever see. Erlang would make writing twitter's back-end FUN.
A dozen crazy Swedish mad scientists slaved over a language for years to enable creating scalable applications like twitter trivial, only to be totally ignored by most everyone until quite recently. And still twitter picks something else for the rebuild.
'Heavy metals poisoning' would seem to be a more apt metaphor than 'silver bullet.'
