it routinely eats up close to 4 GB of RAM, which in my case is an entire VPSes worth and costs me about 60 Euros a year
You are absolutely correct that running other peoples Ruby code is expensive. I would argue similarly for Java because of the high RAM requirements.
However, if you are a company developing your own software, if you use a more productive technology and it spares just 1 programmer then you have paid for a few hundred VMs and running costs become insignificant compared to labour costs.
This is an argument in favour for both Rails and the Java monsters.
You are absolutely correct that running other peoples Ruby code is expensive. I would argue similarly for Java because of the high RAM requirements.
However, if you are a company developing your own software, if you use a more productive technology and it spares just 1 programmer then you have paid for a few hundred VMs and running costs become insignificant compared to labour costs.
This is an argument in favour for both Rails and the Java monsters.