In a few weeks the Xbox LIVE Community Games Channel will be launching, and it has been recently detailed that the time it takes for a XNA community developed game to go from submittion to live on XBL is only 48hours. It is hard to say how well the service will take off from this distance, but time will tell. One thing that is sure however is that if the service provides the functionality and support that is promised, Microsoft will take off ahead of the competition in terms of arcade and indie developed games.
If you are interested in developing with XNA with the Xbox 360 in mind, you should head on over to the community portal and dig around the support provided. Personally coming from a programming background I am extremely exciting with the prospects of the new channel, and only hope that Microsoft aid to create some amazing unique titles. To the normal gamer the channel at least means a ton more arcade themed games each and every week.