[tedsuo]

In short, even "traditional" apps now actually have to do quite a lot of IO, and the ability to cram a large number of requests into a single process can have a dramatic increase in efficiency. If your ruby/php applications are memory bound, you might see a huge increase in availability by switching to node (or any shared-memory concurrency model).

There is no Rails equivalent in node, and in general I would say the community is focused on writing code at a slightly lower level than the high level frameworks you might be used to. But if you feel like you've internalized the RESTful MCV design, you may find the performance increase worth the lack of handrails.