1UP reports that Dungeon Runners, the free MMO by NCSoft, recently updated their game to include forced advertising for it's non-subscribers. Subscriber pay $5 a month to play without ads and enjoy some exclusive content.
With so many MMOs coming to market, I foresee this being the pricing scheme many of them develop to survive: track down advertising dollars (just like radio and TV) and let paying customers play without seeing the ads. This setup will continue to look more attractive to MMO developers and advertising companies as more and more key demographic consumers spend more time playing games and less watching TV. It wasn't all that long ago that I read an EQ2 executive hint that even their game might switch to such an economic model. Dungeon Runners serves as an excellent test run to see how viable such a system will be.