Order categories by most recently updated

This one seems like it would be amazingly obvious and desirable.

Basically I have a client (several actually) who want to list categories (or child cats) and order them by most recently updated. Basically giving the top spots to those most recently updated categories. There are a lot of real basic applications for this, but it’s something that is near impossible to do with WordPress because of the way the taxonomy table is laid out.

So, I’m making a lazy web request for a DB query that would do the follow:

* list all categories (or perhaps all cats of parent X)

* pull out their names and slugs

* list them out in a loop

* but also order them by date

* that date obtained from the posts table, which would pull the latest post in each category just to get the date.

I found similar code here, but it doesn’t work for 2.8:

http://www.devlounge.net/general/last-updated-categories-wordpress-23-query

any ideas?