Hi Hamill,

I did not expect that WebDialogWindow will render rounded corners correctly without server-height.

If you want define height of dialog by content of ContentPane, then you should do that on client. The best option: is to process ClientEvents.Loaded, check actual heights and adjust overall height of dialog from those calculated values. All values can be obtains from public properties.
If your content is more than one control, then to figure out height of that content, I suggest you to wrap content into a single container, for example DIV. You also may set id for that container in order to simplify getting reference to it on client. Below is example.

<ig:WebDialogWindow ID="WebDialogWindow1" runat="server" Width="300px">
     <ClientEvents Loaded="dialogLoaded" />
     <ContentPane>
      <Template>
      <div id="contentOfDialog">
       <asp:Calendar ID="Calendar1" runat="server"></asp:Calendar>
        other controls
    </div>
      </Template>
     </ContentPane>
</ig:WebDialogWindow>

<script type="text/javascript">
function dialogLoaded(dialog)
{
   // instance of $IG.LayoutPane class
   var cp = dialog.get_contentPane();
   var child = document.getElementById('contentOfDialog');
   //or
   //var child = cp.getBody().firstChild;
   //or
   //var child = cp.findChild('contentOfDialog');
   if(!child)
    return;
   // height of dialog
   var height = dialog.get_element().offsetHeight;
   // height of ContentPane
   var cpHeight = cp.getClientHeight();
   //or
   //var cpHeight = cp.getBody().offsetHeight;
   // height of child: your desired height
   var contentHeight = child.offsetHeight;
   // delta to increase/decrease height of ContentPane
   var deltaHeight = cpHeight - contentHeight;
   // final height of dialog
   height -= deltaHeight;
   // optinal 'padding': increase for possible errors
   // height += 5;
   // set height of dialog
   dialog.set_height(height + 'px');
}
</script>