Well, suppose I'll start, though not sure this quite fits. I work for a university, and this year we completed a move of a very sizable portion of our business processes from proprietary software to open source software. The biggest breakthrough was moving some stuff to Drupal (http://drupal.org). Drupal was basically a snowball that picked up steam as it rolled downhill and is now being deployed across campus. 2011 will see it (along with other open source software) taking over the vast majority of our university's apps. The best part has been that most of the effort has come from the ground up with a strong community emphasis.

(With the caveat that Oracle seems to have bought the administration's souls, so it will still be used as the database of choice for many apps for years to come, but eh they own MySQL now too).