WPF: Progress bar with indeterminent duration?

Question

In WinForms you could set a progress bar to loop endlessly to indicate that you don't know how long it will take. How would I do that in WPF?

Answer 1

<ProgressBar IsIndeterminate="True" />

Answer 2

I personally like the approach Visual Studio 2010 takes. They use an animation of a small, looping series of dots (with varying intensity). They just animate the dots circling in the center of the window in question.

In WPF, this is trivial - just animate a rotation of a small drawing of a circle of dots with the opacity set correctly up front.

I find it very intuitive, small, and unintrusive.