We have been working on a new SharePoint provider for Data Synchronisation Studio that makes it now possible to Sync documents and metadata between SharePoint Document Libraries. You might use this provider if you want to migrate between SharePoint 2007 and SharePoint 2010 or just between an on Premise server farm and an Off Premise server farm.
This new provider is the same for Lists or Document Libraries and any custom columns you have on your library are now available.
With Dynamic Columns it makes it really easy to decorate your document Library columns with data, for example you can now pull files from a file share and decorate the metadata from a database and synchronise this to a SharePoint document library. Rather than a Bulk import on Day 1 you can incrementally synchronise changed files and metadata over time.