Home:                                /
About (page):                        /p=10
A Category (archive):                /cat=8
A post of cat num 8 (post):          /p=101

If we go to "A Catogory" - Yes, the li has .current-menu-item class on, and thats good!
But if we go to post-101, the parent-category is not highlighted in the menu. So thats 1 problem.

Lets view another example with menu-childs:

Home:                                /
About (page):                        /p=10
--> A Category (archive):            /cat=8
--> --> A post of cat num 8 (post):  /p=101

if we go to "A Category" or "A Post...", the menu-parent (About) has no .current-menu-item class as well.

That feature is required.
Thanks alot!

I got it to do what you wanted by a combination of function arguments (echo and items_wrap) and processing the output of wp_nav_menu() using the PHP function str_replace().

$args = array(
  'echo' => false,
  'items_wrap' => '<dl id="%1$s" class="%2$s myclass">%3$s</dl>',
);
$subject = wp_nav_menu( $args ); 

$search  = array('<ul', '</ul>', '<li', '</li>');
$replace = array('<dl', '</dl>', '<dd', '</dd>');
echo str_replace($search, $replace, $subject);

You can replace the <ul> tag either in the items_wrap argument or in the str_replace().

Another use that I see is conditional menus based on login status: if your menu is very long, instead of creating multiple ones, you could simply create one and use the exclude parameter to customize each visible version.

There's a technical issue with that everyone should be aware of. Long menus break stuff :/

if your menu is very long, instead of creating multiple ones, you could simply create one and use the exclude parameter to customize each visible version.

Word of warning - Long menus can cause problems. This is a known issue in WP right now, and it's probably safer not to have one massive menu just yet.

The argument is already included in other functions for which your same arguments could be applied.

But those are different functions. wp_nav_menu() has completely different concept behind it. And its concept is to use menu editor to build the EXACT menu you need.

I'm not totally arguing against you proposal. I just think it will not work with the idea of building custom menus. It's a bit awkward if you manually create a menu and then somewhere on the site it does not look like it supposed to. It should be dead simple - create a menu, include it in your template and see it exactly how you configured it. That's what most of users expect it to be.

I am not just thinking about me: I'm sure there are many non-developers out there that could find this feature useful.

wp_nav_menu() function allows you to call a custom walker (see reference). You can use it to achieve your task.

Walkers are for controlling HTML output. I use them all the time, but they seem highly overkill for the purposes described above, don't they?

If you need another menu - create it, it takes only few minutes in menu editor.

That may be your opinoin and/or way of going about it. However, I still think it would be nice to have the option to do it differently. THe argument is already included in other functions for which your same arguments could be applied. Yet, the argument is there. I am only asking to extend it to a very similar function.

The whole idea of wp_nav_menu() is to make creating CUSTOM menus and including them in your theme easy and without any additional coding. If you need another menu - create it, it takes only few minutes in menu editor.