If a post includes an object (e.g. youtube video) it is not shown in the preview pane but the yellow warning banner shows up saying 'Your security settings do not allow Web sites to use ActiveX controls installed on your computer. This page may not display correctly. Click here for options...'
It also threw up an dialog box which I had to get rid of by saying don't show again - so I can't report exact text. Not sure how to get the dialog back on. This was the major annoyance factor.
It seems to take a long time to display the list of unread posts in the preview pane when one of them has an object.
My IE security do allow the object to be rendered and if I browse (within bandit) the post I see the video.