I would like to share my small experience with the freemium model. I have with a friend an online dominoes game where people can play for free but they have to be invited to play. Premium players are the ones who can create new games so in order to play free you need a premium user to start the game.
In my experience, all the author says is completely true. The free users require somehow more maintenance and they are by much the ones that complain more. However, in our case they are the ones that build the site. Without them, the site would be really desolate and premium users would be complaining about the lack of people to play. It would be indeed cheaper to maintain but I am completely sure that the income would be 80% lower.
I don't know if this experience would be helpful for the community here but I thought it would be interesting to share our case where free users are indeed troublesome but completely necessary.