I wrote about it a few times on the NetSol blog, talking about how Mafia Wars gets people to do stuff, as well as how the Mafia Wars gameplay encourages interaction with members of your social network.
There's a lot you can talk about -- casual gaming, the brain chemistry of addiction and gambling, play-acting at transgressive behavior (or actual transgressive behavior, when it came to some developers and affiliate marketers), and most importantly, maintaining contacts via social grooming.
But it also got to be a chore. An essay by A.J. Patrick Liszkiewicz in March, Cultivated Play: Farmville, was still fresh in my mind -- it's all about how one of the rewards of advancing in Farmville is that you don't have to play it as much, as well as touching on obligation and network effects.
So there I was, back in April or May, at whatever level I was at, having just unlocked the Thailand achievement where you achieve top status simultaneously with the Triad and the Yakuza, and then... what? Every additional locale added was just another link to click, revealing another set of arbitrary tasks and achievements.
It ceased having any pretense of fun. So I bailed. Instead of just going idle (which would leave my fairly middlin' to high-level character as a teammate of my friends' Mafias), I went into my own version of "Mafia Wars Witness Protection": I deleted the app, blocked all updates, and didn't look back.
RIP Joelogon Tattaglia
Ultimately, I lasted about a year. I'm not sure what factors, if any, might have kept me in the game -- I'll have to think about that (as will Zynga, no doubt.)