[evilduck]

You don't strictly have to lose interface builder to use RubyMotion, you can use XIBs with Motion, but [for now] addressing elements in the XIB requires a little bit of ugly manual mapping of the numerical XIB element ids to names you want to give them in Motion.

Disclaimer: I've not built anything extensive with Rubymotion/IB, but I have built a proof of concept. I don't know if it's really feasible on a large project.

Also, Obj-C and Ruby share many common concepts, using Cocoa from RubyMotion usually requires just a bit of syntax swapping, "vanilla" RubyMotion is not much of an abstraction.