Can you use MacRuby to develop applications for the Mac App Store?

I have some basic familiarity with Objective-C, but prefer Ruby, so I'm thinking of playing around with MacRuby. Is it possible to use MacRuby to develop applications for the Mac App Store, or do I have to use Objective-C? (Note that I don't care so much about iOS/the iPhone and iPad store right now, just the Mac OS X app store.)

Can you write Mac app in Java?

You have to jump through some hoops. Your app cannot depend on Java being installed on the Mac. You must include a JRE (Java Runtime Environment) within your Mac app. You must write a thin Objective-C wrapper around your Java app.

And to answer the actual question, yes, see http://lists.macosforge.org/pipermail/macruby-devel/2010-November/006475.html.