"Social working" -- I always thought this was the most important takeaways from XP and agile methodologies, that the highest quality work gets done when we tell each other what we're going to do ahead of time (agile/scrum), and then collaborate in the most literal sense by sharing one screen (pair programming) to see that the work gets done in the best possible way. Granted there are surely lots of other takeaways, but those are two things I did take, and I only do one of them.