I'm not an ex IT man, so only rebuild once a year,suprising the power that the CS4 and Lightroom can use.
I've just built my quad core. My hobby however works hand in hand with computers. That being photography. Not as demanding as games, but still requires a computer with a bit of ooomph.
I can now spend the reat of the year using my camera and editing on my pc, knoing full well the pc will handle anything I throw at it, photo editing that is.