If you're on edge Rails and are having problems starting script/console, it may be caused by spaces in your Rails working directory (see ticket 7955: Console environment load broken when RAILS_ROOT contains spaces). Basically the lack of quoting on RAILS_ROOT causes console.rb to pass incorrect paths to IRB (it gets split on the spaces in your directory path).
Just in case anyone runs into this problem and doesn't want to start debugging the problem like I did. Changeset 6512 fixes things. If you do update Rails to revision 6512 (or higher) though, be aware of changest 6507. Ahh the joys of living on the edge.
/opt/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require': no such file to load -- /Data/Working (LoadError) from /opt/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require' from /opt/local/lib/ruby/1.8/irb/init.rb:252:in `load_modules' from /opt/local/lib/ruby/1.8/irb/init.rb:250:in `each' from /opt/local/lib/ruby/1.8/irb/init.rb:250:in `load_modules' from /opt/local/lib/ruby/1.8/irb/init.rb:21:in `setup' from /opt/local/lib/ruby/1.8/irb.rb:54:in `start' from /opt/local/bin/irb:13