I have searched these forums, the help and even google and I can't seem to find any code samples or other help in the use of the OnPropertyChanged.

How and where should I define it so that it replaces functionality I had in old versions from code such as:

Protected Overrides Sub OnCreditLimitChanged()
    Call MyBase.OnCreditLimitChanged()
    CheckRules(Me)
End Sub

which appeared within the CustomEntityCode area of my entity.

Thanks

Does this look right?

Protected Overrides Sub OnPropertyChanged(ByVal propertyName As String)
    Call MyBase.OnPropertyChanged(propertyName)
    If propertyName = "CreditLimit" Then
        CheckRules(Me)
    End If
End Sub

Yes. All you need to do is to use the overrides keyword, and to pass a string parameter.