I concur with the other posters who say Objective-C itself is not the barrier, the API is. Such is the design and verbosity of the API (which is great for self-documentation and talking about, less so for typing), it'd be an absolute nightmare to work with without the extensive auto-complete Xcode offers.

This is a very exciting (and very positive) development, but at this moment in time I would still bite the bullet with Objective-C. I came to it with a background in PHP of all things and didn't struggle with picking it up in a few weeks.

I can't wait to see the things people do with it and with Ruby's metaprogramming.