Microsoft today announced Service Pack 1 for BizTalk Server 2006 R2. Note that this is for the previous version of BizTalk Server, not the current version (BizTalk Server 2009). No doubt a service pack for BTS 2009 will follow in due course.
The service pack is currently at beta. It has only been announced, not released. You can download the beta if you log onto the Connect site.
See http://blogs.msdn.com/biztalkcrt/archive/2009/10/09/announcing-biztalk-2006-r2-sp1.aspx
There are a couple of new features. See http://msdn.microsoft.com/en-us/library/ee532481(BTS.20).aspx.
For a list of bug fixes, seehttp://support.microsoft.com/kb/974563.