Just got this info from Scott Woodgate...

Get it here.  I strongly recommend that everybody trys this in your test environments and then puts it into production.  Along with the usual bug fixes provided in service packs you can expect up to a 10% performance increase in some scenarios.  This is thoroughly recommended and has been well tested by our EAP customer (thanks).

Along with Service Pack 1 we are also releasing the BizTalk Server 2004 Adapter Migration Toolkit. The adapter migration provides interfaces for BizTalk Server 2002 components and adapters such as AICs and Pre-processors. If you are migrating you will find this helpful.