Fresh on microsoft.com downloads, you can get the details of the major breaking changes that occurred for WF between Beta 1 and Beta 2.
Get the document here.
We will publish a similar document for any changes between Beta2 and RTM, although that list should be on the shorter side. If you have feedback on the document, like the way something is presented or think we could have done a better job explaining it, please let me know. Either comment here or use the “Email” link on the side.