A listing of the differences between current models of the Xbox 360 and the new black one announced at E3 last week revealed that the new systems would no longer be able to give the Red Ring of Death. More specifically, it lacked the red light around the power button to display the error; it's not that the system is necessarily invulnerable to suffering the issue.
But the new 360s are smarter about trying to avoid a potential RRoD-style death -- if the system isn't properly venting, the power button will turn red and the system will shut itself off in order to avoid any serious damage. It'll display the message you see above which explains the situation and informs you that the system can be turned back on once the power light has stopped flashing.
It might be somewhat annoying to have your 360 shut off on you in the midst of a play session, but that still seems highly preferable to ending up with the Red Ring of Death and being unable to play for a few weeks while your system is off at Microsoft being repaired.
Source: 1Up.com
