Passive play is practically perfect, right?
The NZ Herald has an interesting feature on Passively Multiplayer Online Games, as they call them, which you play by surfing the web.
The idea is for the game to follow people as they surf the web, giving them experience points, levels, items and currency. PMOG layers social gaming on top of web browsing. Unlike the online strategy games, you don't need to continually return to your habit.