Better classes for menus

@Snugug, @ChinggizKhan, would you be open to take a patch to provide better classes for menus?
For instance: .root, .submenu, .mlid-[menulinkid]...

Not sure if something like that belongs to the base-theme, but it's worth considering...
I'd override theme_menu_link and theme_menu_tree and make sure the structure is as much backwards-compatible as possible.
There's also the possibility to provide a setting in the theme configuration to enable/disable this, but I'm afraid the performance hit would need to be measured before going forward with something like that.

thanks