Looking at this post on NeoGaf http://www.vgchartz.com/forum/thread.php?id=90820&page=1
I expect that the 360 investment will achieve break even results in MS FY2011 (Currently we are in MS FY2010 Q2. FY2011 starts July 1 2010.). This will be results from MS FY2006 through MS FY2011. From that point on the 360 will just be bringing in profits most likely in the $2B per year range and probably has 2-3 years doing that.
Its libraries that sell systems not a single game.







