[megaduck]

I've worked with Eno (the OP) on the product that he's talking about (Cloud Foundry). It's worth noting that the first versions of Cloud Foundry were written in Ruby/Sinatra for the reasons that you're talking about.

We switched to Go because Ruby's concurrency model was obtuse/inefficient and scaling the codebase was challenging even with excellent developers and great engineering practices. The performance gains with Go were a really nice bonus.

If you're solving Google-style problems like writing a PAAS, then the benefits of Go outweigh the headaches. If you're writing a more straightforward CRUD-style Web API, then Rails might be a better choice.