Silverlight 5 enables support for multi-click input on left and right mouse button making it easier to implement features like double click. ClickCount is available on MouseButtonEventArgs.
Drag a rectangle or button on the MainPage.xaml for example and wire up the following Event Handler.
private void ClickMe_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
if (e.ClickCount == 1)
System.Diagnostics.Debug.WriteLine("Single Click");
if (e.ClickCount == 2)
System.Diagnostics.Debug.WriteLine("Double Click");
if (e.ClickCount >= 3)
System.Diagnostics.Debug.WriteLine("Triple Click");
}