http://geekswithblogs.net/JayKinker/archive/2008/10/02/biztalk-server-2009–whats-new.aspx
Microsoft Press Pass: Q&A: What?s Next for BizTalk Server (Sept 5, 2008)
Quotes from above:
It delivers a full upgrade to enable customers to take advantage of the latest platform wave (delivered through Windows Server 2008, Visual Studio 2008, SQL Server 2008, .NET Framework 3.5). In particular the platform updates enable greater scalability and reliability, new Hyper-V virtualization support,