How to create wrapping menu tabs with CSS in Omega
It appears that the default system.menus.css in Drupal sets the white-space property to:


white-space: nowrap;


The default value for white-space is normal.  So, if you set the white-space property on your menu's UL to white-space:normal they will wrap when your screen size gets smaller.

I placed the following in my global.css.


ul.primary {white-space: normal; }