This week's edition of The Escapist has a feature-length article on the Alternate Reality Games movement, focussing specifically on Mind Candy's Perplex City.
The text claims that entertainment is moving towards a "more immersive, participatory experience". While I would concur with that statement on certain levels, I think that regardless of the MySpace-ization of media consumption (i.e., the popularisation of blogs, widespread bulletin boards and easy-to-adapt personalisation) there's a minority of people who want to get actively involved with their entertainment. People want it to wash over them. How else can you explain the continued linearity of most widely-accessible adventure games?
More info on ARGs from the gamesblog can be found here.