How to assign a WP 3.0 custom nav menu to a theme’s navigation menu location via script?

If you’ve already found an answer to this that works well for you, I encourage you to post it here for others to see. If not, the way I would go about it would be to use a custom filter or an action.

Where the menu is output in the theme, either use apply_filters or do_action to trigger the override you want, and in your plugin, hook into that action/filter to output the override. This is a more non-destructive way of accomplishing the same task, as you then don’t overwrite a menu association.