When more than one item is selected, shouldn’t the Info panel allow entries that can (where logically possible) apply to all items? This seems to be the normal OSX behavior (iTunes, e.g.).
That is, you want to give a group of items the same Comment or URL or other; you select them all and enter the appropriate item in the Info panel.
Furthermore: Something like “multiple selection” should show up in the metadata fields if several items are selected. Now they become empty as if no record was selected.