As MacRuby gets closer and closer, with Apple's blessing and support, to 1.0, the question on everyone's lips should be:
When will the App Store (iPhone, iPad and Mac) support ruby applications?
I think it's inevitable. It's an obvious move for Apple, and consistent with the support and attention they've given MacRuby. When it does happen, millions of ruby developers will have an easy way onto the platform. Between this and its natural strengths, the Mac App Store will likely be a very popular platform to build your startup on.