Theoretically, I'm a big fan of this. Rails is huge, and for some applications you certainly don't need it. On the other hand, my practical experience is that

Theoretically, I'm a big fan of this. Rails is huge, and for some applications you certainly don't need it. On the other hand, my practical experience is that every single time I've tried building a Ruby web application without Rails, I end up reimplementing a buggy version of Rails. There are a surprising number of features that are required or desirable in a web application that are really easy to ignore until you realise. YMMV of course, but don't run out looking at things like the new API-only support in Rails too, before you take this approach.