[JohnLBevan]

I recently had a similar idea (i.e. plotting contentment) related to keeping employees engaged / detecting how events at work affected the general mood: https://news.ycombinator.com/item?id=5646466 This post's great as it shows a really good way to model that data (e.g. their use of different colours for days of the week helps to determine if you had a good day for a special reason or if that day people are generally in a better mood).