Thanks for the quick reply! This may already be apparent, but two points are worth noting:
1) The suggested feature could be optional, so developers concerned about the possibility of a <UL> (or something prettier that works without javascript) below the buttons could simply leave the feature turned off.
2) Anything placed between <NOSCRIPT></NOSCRIPT> will not display at all on a browser with javascript enabled. My site is an example:
http://www.frsprod.com
The chief concern here is that sites which require a mouseover to function are fine for the vast majority of users, but it can present real problems to some small but important groups. In particular, sight-impaired users may have a reading device that doesn't deal well with mouseover-activated constructs.