This video from vwestlife on YouTube uses a Kill-A-Watt electricity meter to show that an old PC from 1989 uses about the same power as a PC from 2009. The video was created to dispel rumors that older PCs use more power than modern ones and despite the answer being that both computers use about the same power, the fact remains that the newer PC uses the same power while being able to do significantly more than the old PC.
That's no surprise of course since CPUs have always stayed on the trajectory of doing more tasks at a minimum power requirement. Still, it's interesting to note that power-wise, I guess if you really had to run an old PC, you aren't wasting any more power than you normally would if you just plugged in a newer PC.
Honestly, I'm not sure where I was going with this post. I think I just liked the comparison.