Seems videos will only play on specially registered sites.
All others come up with an unregistered site warning and WPMU link/head screen. Click that and you head off to a registration screen that tells me we can use only allow 20 registered sites.
Pretty useless for a multi-site install and not configurable on a per site basis so I can't even stop the unhelpful message being displayed. I don't think I have missed anything have I? It really is as bad as that?