"While it’s in Google, Facebook, and LinkedIn’s interests to attract as many users as possible – and clearly free is the way – there are obvious consequences: Users get to play without paying, but every few months we get kicked in the face when our digital profiles get abused." - Amber MacArthur, Free sucks. I want my privacy back.
"When you're a free service, you get to say these magic words: 'X is offered as is.' You are off the hook for problems. If people don't like it they can go elsewhere." - Alan Jacobs, Take My Money, Please! The Strange Case of Free Web Services
"Research has shown that humans like getting rewards, but they hate losing what they already have much more than they value the same item as a reward. To be effective with this technique, you have to tell the player they have earned something, and then later tell them that they did not. The longer you allow the player to have the reward before you take it away, the more powerful is the effect." - Ramin Shokrizade, The Top F2P Monetization Tricks
"One of the secrets of success of a F2P game is the implementation of a powerful system of statistical analysis. Game data provides clues as to the users' behavior and preferences." - Pascal Luban, The Design of Free-to-Play Games: Part 1