If you view the following example http://google-maps-utility-library-v3.googlecode.com/svn/tags/markerclusterer/1.0/examples/advanced_example.html in IE10 - it shows the points but not the cluster icons.
Anyone know what the problem is / if there is a fix?
I've had the same issue, you need to add the following code to inside the head section of the page to force the browser into IE9 mode
<meta http-equiv="X-UA-Compatible" content="IE=9"/>
If you are displaying the map inside an IFRAME, then it must be added to the master page.
n.b. You will need to close and re-open your browser in order to see the map working correctly.
For more information see this working example.