It seems that the IE add-in is not working for me on two different machines (XP Pro at home, XP Pro at work - both IE8) and a virtual machine (XP Pro with IE7). The icon is not appearing on e.g. this page:
or the test page I made. I've reinstalled, repaired and rebooted to no avail.
Let me know if there are any details you'd like to know in order to find out what's going wrong.