Instead of putting a label on the optgroups, try adding this to your stylesheet:optgroup + optgroup { border-top: 1px solid black }Much less cheesy looking than a bunch of dashes.
Optgroup labels should describe the group. If a browser implemented on as per the screenshot in the HTML 4.01 spec, then the user would be confronted with rows of dashes and would have to examine each one to find out what was behind it.