1. You have to enter full JIDs, it should default to your domain.
2. When you delete users from your server, it doesn't clean out the MUC affliations of those users.
3. It would be nice if it defaulted to 'Member' type for new additions, but that is a small nitpick. Or at least default to the last type just added on previous page submit. I find myself adding orders of magnitude more members than admins