[Zev]

1. How is the learning curve for a ruby programmer ?

None. MacRuby is an implementation of Ruby 1.9. A very fast Ruby implementation, but, not a completely new language thats only similar. HotCocoa is a gem. A very useful gem that should be the first thing you install, but, a gem.

2. Are using the String and other core classes just the same as ruby, or more difficult / cumbersome.

Just as easily.

3. Can you reuse code from pure ruby apps, or does this re-implementation cause issues/problems.

Sure. Go for it. It is Ruby, after all. Just with an optional gem to access another framework, in this case, Cocoa.