The data exchanges in the Longhorn demo for Commercial Real Estate prompted questions about the way Biztalk, Indigo, and Longhorn work together.

Scott Woodgate's PDC session DAT420: BizTalk Server 2004 with SQL Server “Yukon” DTS and “Indigo” helps clarify (ppt here).  Biztalk will use Indigo as a Biztalk transport for secure, reliable, transacted services.  The Longhorn client will also use Indigo, so you'll have an easy way to connect roaming clients into business processes.