If you are writing ViewModels you will probably need to implement INotifyPropertyChanged, so this article of Brian Genisio might be the right choice to learn a few things about it.
I spend a lot of time writing ViewModels, which almost always implements INotifyPropertyChanged. For those who are not familiar with this interface, it includes a single event: PropertyChanged. That event contains a payload of the name of the property that changed. It exists as a standard way to notify observers that a property needs to be re-evaluated.
Although I use it all the time, I have always believed that INotifyPropertyChanged has some serious shortcomings. One of those shortcomings deals with dependant properties.