I was just playing with nice menus in mayo. I noticed nice menus is referenced in style.css but it does not get themed exactly as the default menu does so I've been working on extending it.
Apologies if this isn't the right place. I've never submitted code before and for such a short snippet this seemed easiest.
My site has the primary and secondary menu enabled, primary left aligned, secondary right aligned, both on the same line of course.
I disabled these and used nice-menu blocks to give the same effect.
I added the following at the bottom of the nice-menus section is style.css and now it displays just like the primary and secondary menu. You have to use nice-menus blocks 1 and 2 of course but most people will be anyway.