A nice little trick to save you always checking for null when firing custom events
Initialize to anonymous delegate.
Ok.. we've an extra call in the invocation list so use judiciously

[code:c#]

public event CompleteTaskExecutionHandler CompleteExecution = delegate { };

//or a sample using Lambdas

public event PropertyChangedEventHandler PropertyChanged = (s,p) => { };

private void Fire()
{
   this.CompleteExecution(...);
}

[/code]

You can now start using the ajax toolkit/library without having any sever support

    <script src="http://ajax.microsoft.com/ajax/beta/0911/Start.js" type="text/javascript"></script>