Asynchronous WPF Commands

Note: The code in this question is part of deSleeper if you want the full source.

One of the things I wanted out of commands was a baked design for asynchronous operations. I wanted the button pressed to disable while the command was executing, and come back when complete. I wanted the actual work to be performed in a ThreadPool work item. And lastly, I wanted a way to handle any errors that occurred during the asynchronous processing.

My solution was an AsyncCommand:

public abstract class AsyncCommand : ICommand
{
    public event EventHandler CanExecuteChanged;
    public event EventHandler ExecutionStarting;
    public event EventHandler<AsyncCommandCompleteEventArgs> ExecutionComplete;

    public abstract string Text { get; }
    private bool _isExecuting;
    public bool IsExecuting
    {
        get { return _isExecuting; }
        private set
        {
            _isExecuting = value;
            if (CanExecuteChanged != null)
                CanExecuteChanged(this, EventArgs.Empty);
        }
    }

    protected abstract void OnExecute(object parameter);

    public void Execute(object parameter)
    {   
        try
        {
            IsExecuting = true;
            if (ExecutionStarting != null)
                ExecutionStarting(this, EventArgs.Empty);

            var dispatcher = Dispatcher.CurrentDispatcher;
            ThreadPool.QueueUserWorkItem(
                obj =>
                {
                    try
                    {
                        OnExecute(parameter);
                        if (ExecutionComplete != null)
                            dispatcher.Invoke(DispatcherPriority.Normal, 
                                ExecutionComplete, this, 
                                new AsyncCommandCompleteEventArgs(null));
                    }
                    catch (Exception ex)