>Take a look at huge websites with a complicated nested navigation like Amazon: most of the time it takes 2 levels.
>If you really need that level of detail you would be better off taking the user from a top or 2nd level choice to a separate page with a second menu. As long as there is a breadcrumb trail so they can navigate their way back you should be fine.
Although I suspect Amazon do it with filter logic and who lot of database management. :)