The number of ISVs who are exploring the potential of developing on the Vista platform is growing all the time. One of the ISVs who have been using Windows Workflow Foundation since the very first betas is K2 who have created an advanced workflow engine which helps organisations rapidly build rich applications which are compliant with company policies.
They've also hooked into the SideBar to provide a great dashboard entry point into the application. I see gadgets being used in this manner as an extension of Vista apps so that users can quickly become aware of changes in business applications that are important to them.
Check out the demo video here.
Read more about Windows Workflow Foundation
Find out why K2 used Windows Workflow Foundation for their application
Understand how to develop Sidebar Gadgets