Brian Harry's posted the final feature list for TFS 2008 (f.k.a "Orcas"): http://blogs.msdn.com/bharry/archive/2007/08/08/final-tfs-2008-feature-list.aspx
A few of my favorites:
- SharePoint 2007 support
- SQL 2008 support
- Simpler installation
- Native CI support
- NET object model for the build server
- Incremental builds & gets
- Get latest on checkout