Sorry if this is old news (but I didn't see any announcements about it). I just upgraded my Wordpress install to 2.2, and noticed in the release notes that the Admin now uses jQuery.
http://wordpress.org/development/2007/05/wordpress-22/ >From that post: "We now use jQuery for a number of internal functions, and hope to transition all of our JS to use it. (We still need volunteers for this.)"
