There is a clear usage by major brands of large dropdown menus and this article by usability guru Jakob Nielsen makes this point in his latest Alertbox post, recommending the use of such menus to improve the user experience, as well as providing some tips on making 'mega drop-downs' more user friendly. Here is an analysis of some sites which I think is very helpful.
My name is Chris Parker. Based in Kent, we provide digital marketing
services for businesses across Kent and beyond. You can find me on LinkedIn, Twitter and Google +.