These few days I have been playing with RubyMotion.
They have documents on using Objective-C libraries. So using familiar library such as TouchJSON is not an issue.
How about using Ruby library such as BubbleWrap? There are no documents on how to include and write gems in your project yet. Before it is ready, you can do this:
-----> Heroku receiving push
-----> Ruby/Rails app detected
-----> Detected Rails is not set to serve static_assets
Installing rails3_serve_static_assets... done
-----> Configure Rails 3 to disable x-sendfile
Installing rails3_disable_x_sendfile... done
-----> Configure Rails to log to stdout
Installing rails_log_stdout... done
-----> Gemfile detected, running Bundler version 1.0.7
Unresolved dependencies detected; Installing...
Using --without development:test
You have modified your Gemfile in development but did not check
the resulting snapshot (Gemfile.lock) into version control
You have added to the Gemfile:
* therubyracer (>= 0.9.8)
* libnotify
* rb-inotify
You have deleted from the Gemfile:
* growl
* rb-fsevent
FAILED: http://devcenter.heroku.com/articles/bundler
! Heroku push rejected, failed to install gems via Bundler