I dare to say that most Ruby code is written in Rails projects and we almost always know were a method is defined, because of conventions (models, views, lib, concerns). It's when the developer is too smart that we get into troubles. The only project where I needed ctags in the last years was a php zend application that I had to get familiar with to be able to design its v2.

So it might be another issue with Rails' influence over Ruby: not many chances to move beyond the fence (me too.)