Granted, there is no magical way to tell whether or not you are one of the alleged 30% of Xbox 360 owners who will suffer the red rings of death. But there is an easy way to check if your unit shipped with the new heatsink Microsoft has added to later units—a feature that we're guessing gives you a much higher chance of survival.
Stick your camera up to the power button side of you Xbox and take a picture with flash. If you see a heatsink (a pile of darkness), good. If you see an empty space and a DVD drive (like in this picture), bad...and your days are probably numbered, my friend. [benheck via kotaku]