Honestly, I don't know that I will uprgrade if and when the new systems come out. How much more advanced can games get? The PS3 and Xbox360 , and for that matter the Wii for what it does, are great machines.
Unless game designers just stop supporting the 360 that is the system I will be playing for the foreseeable future, with occasional PS3 gaming, and the Wii for my kids.
But yes the xbox is really a great console. I have both PS3 and Xbox and have been using xbox more lately. Not sure if it is just because I feel like I paid money for the online so I should use it or what. But other than my controllers randomly disconnecting its a great system.