Add class/other to “current” menu item, wp_nav_menu()

Haven’t been hacking in quite some time. Very excited about Menus and Types, but have this question:

Given a Pages list, or perhaps a new custom menu, how can I add an HTML class or wrap the given item somehow, for the “current” page.

IE, I on the Pages list/menu, if my users are viewing the “about” page, I’d like to add a ‘current’ class/style to the “About” page menu item.

What hook should I be looking at, or is this not implemented yet?

Thanks!