Nick on Silverlight and WPF has posted a couple more bits of code about ChangeableObject and ValueConverter that others might find useful.
Nick:
Whenever I do databinding-intensive apps (both Silverlight & WPF), I find myself writing a fair amount of boilerplate code. If you want change notifications on your class, you need to inherit from INotifyPropertyChanged, define a PropertyChanged event, and write a couple lines of code to fire it.