I think there are some definite interesting possibilities for cloud computing to enhance gaming, especially multi-player and social gaming, with persistant world integration. GaiKai like features are also possible for certain situations. Of course this is not necessarily something that benefits from a 'platform holder', but is something that is inherently available to all who are willing to invest in writing the necessary software and finding a hosting partner/host yourself, so the question is what Microsoft brings to the table ...