Not very much. While my G4 Powerbook is in dire need of replacement (and will be replaced soon), my 24-inch iMac is fast enough for anything I can throw at it. What takes time is when the computer is waiting on me, not vice-versa. It's good enough, even for someone doing fairly intense work.
Camera companies are getting windfalls right now because, with the advent of digital, cameras aren't good enough anymore. It's ironic: The Nikon F100 was good enough, but the cameras that replaced it, being on the bleeding edge of technology, aren't. In the past year or two, we've seen digital cameras that by most definition really are good enough for pretty much any work, but not from the perspective of technology -- e.g. new cameras are still being released all the time with updates that give genuine new opportunities. Think that 1D Mark II was good enough? Meet the 1D Mark III.
So when will we get cameras that are so good that they actually hurt the makers? Cameras that few even want to replace after a couple years? Like everything that has happened with digital photography, I think that benchmark will come sooner than most think, and I'm sure the camera-makers are sweating about it. But it's great news for us.