I’ve added rel='me' attributes to the links in my navigation menu. Step one in the indiewebification of this site. Yeah!
If, more generically, you’re curious as to how to one would go about adding attributes a WordPress menu item, may I point you in the direction of a few resources. Here’s your man, Neil Gee, laying it out pretty simply. Essentially, you create a function in your theme’s functions.php file that returns the attributes that you want to add. You then call that function using the add_filter() function and voila.