What is the best practice to deploy SPD workflow into production?
This got a little better in SharePoint 2010. You can save a reusable workflow as a .wsp (SharePoint solution file) and publish it on the server that way. Works best if you have Visual Studio. I haven't tried it without it, but I might just to see how it works.
There is a walk-thru on the MSDN site at: http://msdn.microsoft.com/en-us/library/ee231580.aspx
There are some other suggestions at: http://social.technet.microsoft.com/Forums/en-US/sharepoint2010customization/thread/3ccc0692-4fe7-4ef1-a311-fae29e7afdad