I've written a lot of both Ruby and Objective-C/Cocoa over the last few years, and as much as I enjoy working with Objective-C Ruby really would save a lot of effort. It's not like I have a problem "moving away" from Ruby, but I'd like the option to sell apps made with it through their service.
If Apple ships MacRuby pre-installed in Lion, with Xcode integration and documentation, I think it would be huge.