Jesse Liberty explains how with element binding it is now possible to bind the value of one object in your UI directly to a second object, without recourse to binding to a data object or handling events.
Until Silverlight 3, the easiest way to get this to work was to bind both the Slider and the TextBlcok to a data object. When the slider’s value changed, a property in the data object would be modified, and the TextBlock, also bound to that property would be updated (assuming you had implemented the INotifyPropertyChanged interface as discussed here. This can still be done, but now you can leave out the data object.