This question was presented to me over at Peerpong:
"What is the social or psychological factors which lead people to be drawn into investing huge amounts of time into casual games, IE FarmVille?"
I personally divide online casual games into two camps. There are the traditional casual games such as poker, fortress, tetris, pool, memory, etc. The second camp is what I define as "lazy casual games" or lazy interactivity (borrowing from the interactive TV space). This is a new genre of casual games, such as FarmVille and Mafia Wars, that are almost as mindless as channel surfing late at night when you're almost asleep.
It's lazy interactivity because it takes very little movement (i.e. clicking the mouse without precision) to play these games. You can almost be in a daze to successfully play FarmVille or maybe you're multi-tasking on two projects, eating and talking to your spouse.
These "lazy casual games" entice people with enough simple rewards or a sense of accomplishment in exchange for the perceived effort put into it, so it's a low bar for these games to satisfy the typical game player. It's similar to the offline enticement of winning tickets at Dave & Buster's or a local carnival by whacking moles or shooting water into a balloon in exchange for stupid plastic toy prizes, candy from the 1960s (literally), or tin medals.
The interesting thing for me to see would be the churn rate. How long does the average person play FarmVille and other similar games? What is the lifespan of these casual games? Do they have staying power like a traditional casual game, such as Tetris? Do people come back after they stop playing or do they never play again after the first time they stop?