ExecuteResult is a method on the System.Web.Mvc.ActionResult class. Are you sure you don't mean to be looking there?
http://aspnet.codeplex.com/SourceControl/changeset/view/23011#266522
The Model property is just an object type, and always has been, AFAIK.
As for updating the table, what I've done in the past, to update a portion of a page after a partial view is to use Ajax.BeginForm like so:
<% using (Ajax.BeginForm("Customers", new AjaxOptions { UpdateTargetId = "customerList"})) { %>
<!-- FORM HERE -->
<% } %>
<div id="customerList">
<% Html.RenderPartial("CustomerList"); %>
</div>
'UpdateTargetId' is the key here, and tells MVC to use the result of the "Customers" action to replace (by default, you can append by setting the InsertionMode AjaxOption to InsertBefore or InsertAfter) everything inside the element withthe Id you specify.
If you want to use the same action to service the full page request and the Ajax request, you can use the IsAjaxRequest extension method to determine what to return:
if (Request.IsAjaxRequest())
return PartialView("CustomerList");
// Not an Ajax request, return the full view
return View();
Hope that helps!