Check out what happened when AJAX bug tags editing landed in April:

Note that since Launchpad has the edge/production split, so the changes in the graphs are less drastic since a set of users start interacting with new code before others.

Check out UDS helping out the Gnome Zeitgeist developers: http://seilo.geekyogre.com/2009/06/udss-influence-on-gnome-zeitgeist/