For no other reason than curiosity I decompiled a nice big chunk of BTS06 over a coffee break. You can’t decompile BTSNTSVC.exe unfortunately but the messaging assemblies etc are just all IL waiting to be disassembled. You can decompile HAT too.
Now if only we could get hold of that magic 31bf3856ad364e35 key. Just kidding… 😉
Oh, and be sure to checkout the BizTalk decompiler on CodePlex that will help you decompile an actual BizTalk assembly complete with orchestrations, maps, etc…