And the actual error. I eliminated any sort of problem of UNIX permissions by chmod public and data (assuming that Glassfish is running as a different user).
Processing UploadFilesController#upload (for 192.168.1.186 at 2010-01-28 20:18:22) [POST]
Parameters: {"authenticity_token"=>"C+urlXkILnfnj7Bb2OOPzE7G0omAuVmNJMEuWJ/crL4=", "upload_file"=>{"data"=>#<File:/tmp/RackMultipart.284.53931>}}
IOError (No such file or directory):
app/controllers/upload_files_controller.rb:18:in `initialize'
app/controllers/upload_files_controller.rb:18:in `open'
app/controllers/upload_files_controller.rb:18:in `upload'
file:/Library/glassfishv3/glassfish/modules/grizzly-jruby.jar!/rack/adapter/rails.rb:133:in `call'
file:/Library/glassfishv3/glassfish/modules/grizzly-jruby.jar!/rack/handler/grizzly.rb:55:in `call'
:1
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