Definitely. I timed the existing site_node_closest_ancestor_package proc (which, it looks like, is being run on every single page hit on greenpeace.org), and it took anywhere from 750 to 2500 microseconds on our box.
The good thing is that there's no database hit involved.
I'm thinking that we could simply include the nearest subsite_id in the internal site_node data structure that we already have.
/Lars
