a recent article over at Gamasutra, Sony Online Entertainment's Executive Producer Matt Wilson explains some of the challenges they face with getting an MMO truly cross-platform. With the upcoming spy MMO The Agency being released on the PC and Playstation 3, they've run across some obstacles during development, but they're probably not the ones you'd expect.
Wilson explains that it's not so much a technological problem between the two platforms, it's more an issue of regular updates. On the open platform PC, developers can release immediate updates and patches to correct problems, balance game mechanics or introduce new content. On the closed platform console, they would need to go through a certification process first. This could cause quite a problem for a genre of gaming that lives and breathes by its regular, immediate updates.