Yes, I used jQuery to do this on
CISP - as you can see by attempting to navigate through the left navigation on the site.
Anyway, I believe I used
this plugin. As you can see, it's pretty effective.
Note to smw: I'm pretty sure the navigation on CISP is what you described. As you can see by navigating within that site, I was able to keep the "category" open from one page to the next.
Alex