rails new

gave me this:

Installing coffee-script-source (1.6.2)
Errno::EACCES: Permission denied – /Library/Ruby/Gems/1.8/build_info/coffee-script-source-1.6.2.info
An error occurred while installing coffee-script-source (1.6.2), and Bundler
cannot continue.
Make sure that gem install coffee-script-source -v '1.6.2' succeeds before
bundling.

Note: see the previous post on installing Rails if you are having Rails problems.