The first Community Technology Preview (CTP) for the WF Migration Kit has been released, for migrating to the upcoming new Windows Workflow Foundation.
Consider trying the tool if you are a WF3 user who is looking to migrate your workflows to WF4. Migrators are included for a number of the WF3 out-of-the-box activities. There is also an extensibility point that allows the authoring of custom migrators for handling custom activities.
There is also further WF3 to WF4 migration guidance here.
[I will also point out that since this release is through CodePlex the source code is available as well.]