font-weight: normal; so that it doesn't look like a big fat over-bolded mess. This works fine unless the user doesn't have Impact or Arial Black, and unless your backup fonts are all bold by default, they'll get a heading that is un-bolded and wimpy due to the CSS rule mentioned above.
Is there a workaround for this? I couldn't think of one, and it's a bummer especially since Impact and Arial Black are fonts that many users have -- and lend themselves nicely to further CSS styling tricks. Also, if anyone has a better way of conveying "un-bolded" or "over-bolded"...