PersistenceManager now contains an overloaded InvokeServerMethodAsync method which allows for asynchronous invocation of a server-side method.  This method works similarly to the synchronous InvokeServerMethod, except that the method return data is available in the event arguments passed to the InvokeServerMethodCompleted event.  An outstanding request can be canceled using the CancelAsync method.

    private void MakeAsyncCall() {

      PersistenceManager pm = PersistenceManager.DefaultManager;

      // Setup completion handler

pm.InvokeServerMethodCompleted +=

new EventHandler<InvokeServerMethodCompletedEventArgs>(InvokeServerMethodCompletedHandler);

      // Make async call

      Guid myToken = Guid.NewGuid();

      pm.InvokeServerMethodAsync(new ServerRpcPersistenceDelegate(Order.GetNumberOfOrdersSlow), myToken,

         new DateTime(1995, 1, 1), new DateTime(1999, 1, 1));

    }

    private void InvokeServerMethodCompletedHandler(object sender, InvokeServerMethodCompletedEventArgs e) {

      Guid token = (Guid)e.UserState;

      if (!e.Cancelled) {

        MessageBox.Show("my async result = " + Convert.ToInt32(e.Result).ToString());

      }

    }

 There is also a Tech Tip which you might find relevant:

http://www.ideablade.com/techtip_Extract_Maximum_Data_Retrieval_Performance.htm