interpolation for the url when storing paperclip attachments on s3 that works independent of where your bucket is located.

paperclip_s3_fix.rb

# normally paperclip uses the server/bucket/location format, but that breaks when you have a eu bucket. 
# This one works for all buckets.
# put in an initializer (or somewhere else) and add this to has_attached_file params
#  :url => ':s3_url',

Paperclip.interpolates(:s3_url) { |attachment, style|
  "#{attachment.s3_protocol}://#{attachment.bucket_name}.s3.amazonaws.com/#{attachment.path(style).gsub(%r{^/}, "")}"
}