Migrating from WF 3.0/3.5 to WF 4.0
A full set of documents have been released at the beginning of the year to suggest migration strategies of legacy WF 3.0/3.5 code to the new WF 4.0 platform. You may download them all here. Documents seem to refer to version beta 2 of WF 4.0 and thus a few details might have changed in the final release of the new WF 4.0 technology. Along with these documents, code samples have also been released on Codeplex.