Ported from the PHP code at valums.com/ajax-upload/
In your Gemfile
gem "qqfileuploader"
In any action you wish to process a ajax upload, use this helper method
handle_upload(upload_dir, replace_file, options...)
It returns the a hash ready to be json-ified and returned back to the client. Optional arguments include:
:allow_extensions => [array of file extensions] :size_limit => int, max file size (defaults to 10485760 bytes)