When a new console is launched I try to buy it as soon as possible with a fairly random good game to start over a new gen.
I did it since the PSone era all along to this one, and the instant I buy a new system, my old system will inevitably die. I'll play it some little here and then just for the nostalgia since the new system is backwards compatible.
This gen I wanna max out the life my consoles will have, so for the case of Microsoft,
I'll upgrade if\when a flight simulator launches with "next Natal" support.
What about you? You'll buy it day one or will wait for a specific game that completely amazes you to jump in a new era?