Last week the final version of the Windows Server 2008 SDK went online. If you've been using the beta SDK releases for Orcas samples or tools, then this is the version of the SDK that you'll want to install. Here are the links to the download materials:
I don't have any particular known issues to call out for WCF other than that some of the SDK tools require that you have Orcas installed. If you're developing Windows Server 2008 applications but don't want to upgrade to Orcas, then you can grab the appropriate tools from one of the previous Windows Vista SDK releases.