As my good friend pointed out - Rahul Garg, the BizTalk 2009 documentation is available for public download.

Things such as:

• runtime engine
• mapping
• Orchestrations
• Adapter V1.0 Frameworks
• BizTalk Applications
• BizTalk Deployment of Applications

Have all generally (obvious fixes and improvements as needed) stayed the same.

Whereas, a quick summary of things I'd be looking for in the documentation:

• Incorporating BizTalk Project builds into automated tested suites (TFS etc) - Biztalk 2009 projects can now be built through MSBUILD as a regular project in the solution.
• Individual components such as Schemas and Maps can be formally unit tested (previously we wrote our own helper classes to make this stuff happen) - although, at the moment when testing a schema, I haven't been getting back details of the error...just a pass/fail.
• BizTalk Adapter Pack 2.0 (Sql, Oracle x 2, SAP, Siebel...) - based on WCF channel stack...very nice! (can be standalone if needed)
• WS Federated bindings
• and the list goes on.....

Download a Searchable BizTalk Help File - very handy to have when planning your upgrades or migrations.