This post of the series of Sergey Barskiy on Silverlight 3 is all about ElementName binding.
Probably my favorite feature in Silverlight 3 that affects developers writing business applications is addition of ElementName property to Binding object. This features existed in WPF since version 1, but was missing from Silverlight 2.0. The basic strategy behind the feature is the ability to bind a property on one UI element to a property on another UI element. Here is a very common scenario in a business application that this features makes much simpler to implement. Say, you have two co-dependent combo boxes. For example, you have a combo box with a listing of states, and once a state is selected, second combo box is populated with a list of cities for that state.