Performance is impacted: some machines spin 25% CPU while the browser is idle: that's why I'm trying to find the fix. Further testing has shown that it is something in my Site.Master and not the child pages with the grids. Site.Master contains a few WebTextEditor (read-only) and a WebDataMenu. Due to a previous IE7 issue with the WebDataMenu (appearing behind grids in child pages when expanded) I added

function IE7ZIndexAdjust() {
  var div1 = $get('MenuDiv');
  if ($util.IsIE7) {
    div1.style.zIndex = '10';
    div1.style.position = 'relative';
  }
}

<div id="MenuDiv">
<ig:WebDataMenu ID="WebDataMenu" runat="server" Width="1015px" GroupSettings-EnableAnimation="False" EnableExpandOnClick="True">
<ClientEvents Initialize="IE7ZIndexAdjust" />
<GroupSettings Orientation="Horizontal" />
</ig:WebDataMenu>
</div>

I removed the ClientEvents but that did not correct the phantom CPU usage in IE7 mode while the page is idle. I'll start playing with settings in the WebDataMenu but can you look at it too?

FYI, the menu items are built in code-behind using data from SQL. For example:

WebDataMenu.Items.Add(new DataMenuItem {Text = "Functions"});
DataSet results = Common.GetDataSetSQL("EXEC [dbo].[SPNAME] '" + sParam + "'");
if (results.Tables["TBNAME"].Rows.Count != 0)
{
  foreach (DataRow rowSQL in results.Tables["TBNAME"].Rows)
  {
    WebDataMenu.Items[iMenuIndex].Items.Add(new DataMenuItem
    {
      Text = rowSQL["Text"].ToString(),
      NavigateUrl = "/" + sAppRoot + "/" + rowSQL["NavigateUrl"].ToString()
    });
  }
}