Ok, so spawn doesn't work exactly right yet.

lib/paperclip.rb

@@ -60,7 +60,8 @@ module Paperclip
         :whiny_thumbnails  => true,
         :image_magick_path => nil,
         :command_path      => nil,
-        :log               => true
+        :log               => true,
+        :swallow_stderr    => true
       }
     end
 
@@ -84,7 +85,9 @@ module Paperclip
     # expected_outcodes, a PaperclipCommandLineError will be raised. Generally
     # a code of 0 is expected, but a list of codes may be passed if necessary.
     def run cmd, params = "", expected_outcodes = 0
-      output = `#{%Q[#{path_for_command(cmd)} #{params} 2>#{bit_bucket}].gsub(/\s+/, " ")}`
+      command = %Q<#{%Q[#{path_for_command(cmd)} #{params}].gsub(/\s+/, " ")}>
+      command = "#{command} 2>#{bit_bucket}" if Paperclip.options[:swallow_stderr]
+      output = `#{command}`
       unless [expected_outcodes].flatten.include?($?.exitstatus)
         raise PaperclipCommandLineError, "Error while running #{cmd}"
       end

lib/paperclip/attachment.rb

@@ -353,11 +353,11 @@ module Paperclip
     # When processing, if the spawn plugin is installed, processing can be done in
     # a background fork or thread if desired.
     def background(&blk)
-      if instance.respond_to?(:spawn) && @background
-        instance.spawn(&blk)
-      else
+      # if instance.respond_to?(:spawn) && @background
+      #   instance.spawn(&blk)
+      # else
         blk.call
-      end
+      # end
     end
 
     def callback which #:nodoc:

test/attachment_test.rb

@@ -232,19 +232,19 @@ class AttachmentTest < Test::Unit::TestCase
     end
   end
 
-  context "When spawn is defined on the instance" do
-    setup do
-      Dummy.any_instance.stubs(:spawn)
-      rebuild_model :styles => {:foo => true}
-      @dummy = Dummy.new
-      @file = StringIO.new("12345")
-    end
-
-    should "not call spawn on the instance when assigned a file" do
-      @dummy.expects(:spawn)
-      @dummy.avatar = @file
-    end
-  end
+  # context "When spawn is defined on the instance" do
+  #   setup do
+  #     Dummy.any_instance.stubs(:spawn)
+  #     rebuild_model :styles => {:foo => true}
+  #     @dummy = Dummy.new
+  #     @file = StringIO.new("12345")
+  #   end
+
+  #   should "not call spawn on the instance when assigned a file" do
+  #     @dummy.expects(:spawn)
+  #     @dummy.avatar = @file
+  #   end
+  # end
 
   context "An attachment with no processors defined" do
     setup do