Lately I’ve been playing with Korundum. It’s nice, it works very well and combined with KDevelop it’s a very powerful RAD.
The big problem is the lack of documentation: I’ve read Caleb Tennis’ Rapid GUI development with QtRuby and it’s a wonderful introduction, but I miss a book going deeper into QtRuby/Korundum. This is not to say it’s worthless, quite the contrary: it’s the best $8.5 I’ve spent in months.
However, the “enterprise” learning is coming from reading others’ source code (I’ve been googling for qtruby, korundum; searching Rubyforge, etc) and from Richard Dale (via #qtruby in freenode). Once again, thank you so much Richard for such a good development environment!