Do you remember my Astoria Blog Publishing post? well now you can check that my crystal ball is up and running!
Cool to see that any SharePoint Server 2010 acts as a Data Services Server
So moving forward that vision would look like this, after installing latest ADO.NET Data Services in your SharePoint 2010 sandbox, imagine you create a blog site /carloshm, then you will be able to get the categories at /carloshm/_vti_bin/ListData.svc/Categories. That simple.
Check this article, as it would be worth reading! to start using it