Changed the sanitization a little.

lib/paperclip/attachment.rb

@@ -58,7 +58,7 @@ module Paperclip
       return nil if uploaded_file.nil?
 
       @queued_for_write[:original]        = uploaded_file.to_tempfile
-      @instance[:"#{@name}_file_name"]    = uploaded_file.original_filename.strip.gsub /[^A-Za-z0-9\.]/, '_'
+      @instance[:"#{@name}_file_name"]    = uploaded_file.original_filename.strip.gsub /[^\w\d\.\-]+/, '_'
       @instance[:"#{@name}_content_type"] = uploaded_file.content_type.strip
       @instance[:"#{@name}_file_size"]    = uploaded_file.size.to_i
 

test/test_attachment.rb

@@ -137,7 +137,7 @@ class AttachmentTest < Test::Unit::TestCase
     end
     
     should "remove strange letters and replace with underscore (_)" do
-      assert_equal "sheep_say_b__.png", @dummy.avatar.original_filename
+      assert_equal "sheep_say_b_.png", @dummy.avatar.original_filename
     end
     
   end