At your own peril : (I don't have other users on our MU install than myself, so security is not an issue)
Put in these tags and something along the lines of the below code into your "allowed" arrays in kses.php :
object, embed, param, script.
This will allow video embeds from most providers, incl. YouTube, Google Video, Viddler, Blip.tv and others as well as widgets from a lot of sources. It works on posts imported by FeedWordpress for instance, which was my problem with the "Unfiltered MU" plugin.
'object' => array (
'id' => array (),
'classid' => array (),
'data' => array (),
'type' => array (),
'width' => array (),
'height' => array (),
'allowfullscreen' => array ()),
'param' => array (
'name' => array (),
'value' => array ()),
'embed' => array (
'id' => array (),
'style' => array (),
'src' => array (),
'type' => array (),
'height' => array (),
'width' => array (),
'quality' => array (),
'name' => array (),
'flashvars' => array (),
'allowscriptaccess' => array (),
'allowfullscreen' => array ()),
'script' => array (
'type' => array ()),
Email me at morten@kaplak.com for my altered kses.php if the above has become too distorted to make sense of by this comment form.