I fully agree with Flake. My first digital was an S20. Coming from a Pentax LX with a rich set of lenses, the quality of those digital images was, per se, awful, but it was easy to understand the huge potential of the new technology. So, I was very happy to trade the S20, in few months, for a G1. In less than a year a new exchange was largely justified by the improved quality performed by a Nikon 5700. Next step, the following year, was a 350D, that allowed me to reenter the reflex+lenses range. It needed three years for the next step, 50D and one year for a 5D MkII and four L lenses. Each of these steps was justified by the big improvement in IQ. Recently I added a 1Ds MkIII, but, I have to say, that didn't mean a great improvement. I suppose, so, that the improvement of digital photography is reaching its top, until something really revolutionary will come.
If I have a look at great photographers portfolio, I can't imagine that the quality of their images could in any way improved by a new camera. Not enough, at least, to justify the anxiety manifested by many people in this forum to get a new model, since I can't believe that the market and R&D are ready, in these difficult times, for a real revolution, able to radically improve the quality of our pictures.
And a large depreciation of our equipment does not seem so desirable, if not for a real and substantial progress.
Different conclusion, obviously, if for us a new camera is something to treat ourselves like it would be for a new toy, but this is something quite different from a real and useful tool...