See http://msdn.microsoft.com/en-us/vsts2008/products/bb725993.aspx or http://blog.accentient.com/2010FeaturePreviewForTFSVSTS2010.aspx or http://bryanandnoel.spaces.live.com/Blog/cns!80E4A0EADF0C523C!1576.entry for some commentary on planned features for TFS 2010. Some things I like include:
1. Finally we get hierarchical Work Item relationships.
2. Linking of work items to each other and other objects is much more user-friendly.
3. Build agent pooling lets you define a pool of build machines instead of individual build servers. This feels a lot like pulling your build machines from the cloud.
4. Build workflow is vastly improved. For example, parallel building from one agent.
5. A new Agile process template.
6. Rollbacks really work right in SCC.
7. Modeling that works with code. The planned Architecture Layer Diagram means that a developer or architect can use models to enforce constraints on code as well. The Architecture Layer Diagram can be coupled to code making it an active diagram that can be used for validation.
8. A new Test Impact View window enables a developer to view a list of tests that need to be run as the result of a code change.
9. Eliminating "No-Repro" bugs. I'll believe it when I see it.
10. Branch Visualization is improved – basically a variety of graphical ways to see branching. Branches become a first class citizen and show up in Source Control under a different icon (no longer just a subfolder structure). You can visualize the hierarchy. You can also visualize the way a changeset has been merged through the branch structure to help you see if a parent or child has been missed.