I've been playing with mruby for the past week or so. If you haven't seen it yet it is an embeddable version of Ruby. The first thing I wonder about when I heard about mruby last year a RubyConf was embedding it in iOS apps. Now that the initial version has been released I figured I would give it a try.
There are a few things to take into account before diving into this. The first is that the mruby project is very new and there are a number of gaps in the language support right now but the goal is to support the ISO definition of Ruby at some point. The second thing to know is that I'm talking about embedding Ruby here and not writing iOS apps using Ruby. I'm more interested in the potential of Ruby as a scripting language for something like a game. If you want to look into writing iOS apps using Ruby check out RubyMotion or the MobiRuby project (MobiRuby is based on mruby).