2009-Feb-15:  When looking for a menu-bar / nav-bar, the "Suckerfish" CSS dropdown menus came close to what I wanted.  However I wanted something that would work visually together with centered elements.  I also wanted something that was easily changed, without any laborious recalcaulation of widths.  Rather than simple centering, I found that I preferred to have it behave in the style of a justified paragraph (the distinction will become clear when considering a menu-bar needing multiple lines).  I abandoned doing it in CSS, and wrote some Javascript to do it.  The CSS is the work of others, part of the Javascript is too -- see the credits in the CSS and JS files.

Here is the CSS.

Here is the Javascript.

An example of a site using it  (resize your window while viewing it to appreciate the behaviour).

Upon upgrading my Opera-browser from version 9.63 to 10.11, I noticed that these suckerfish-based menus misbehave under Opera-10.11 -- the dropdowns fail to go away when they should, although they do on a Reload.  I'm not aware of any other browser having that problem, but will attempt to solve it for Opera-10.  Googling for a solution wasn't fruitful; looks as though other people's suckerfish-style menus are working in Opera-10, in fact one person states that Opera-10 is the first version of Opera for which his work correctly. 

These menus still work as desired in Firefox-1, Firefox-2, Firefox-3 (after "KLUGE-3.6"), Opera-9, ie6 (under wine), ie7 (under wine).  They misbehave in Konquerer in what looks to be a worse case of the Firefox-3 problem, not the Opera-10 problem.

Shortly after I'd gone to Opera-10.11 another new version, 10.60, became available, and I promptly upgraded to it.  However it was such a disaster that I felt forced to go back to an earlier version, and going back to 9.63 was just as easy as going to 10.11 so that's what I did, and thus getting these "suckerfish" menus working in Opera-10 lost its urgency.