Non-Blocking UI WPF/Silverlight

What are the things to be kept in mind while designing a non-blocking UI. Is IObserva开发者_如何学Pythonble meant for that?

There is also very interesting idea of coroutines when working with async methods.

You can read abut it here:

1. Asycnhronous Service Calls with Coroutines
2. Coroutines with MVVM Light
3. IResult and Coroutines

I think most general rule would be: All long-lasting operations, like database or service calls should be run either asynchronouly or in separate thread or backgrounworker.