I am always afraid to mention this being afraid that if too many people realise what I am going to say now eventually this will no longer be true but...
This is a problem if you buy new, it is great if you don't mind buying second hand (I don't).
A Canon EOS5d produces still great pictures and can be bought for something less than 800 US$ only because there exist a Mark II and now a Mark III version of the camera. For people using cameras to show off maybe it's not good but for the rest of us taking pictures these "obsolete" cameras are just great. Similar examples can be found in the Nikon, Sony, Pentax whatever line of cameras.
Ok, maybe someone really needs 38 megapixels or the fastest autofocus but for a lot of professional work as well as most of what you might want to shot for fun they are just fine. I use for most of what I do a Fujifilm S5Pro with a Nikon kit lens (it used to be considered good, it is the 18-70 3.5-4.5 G ED, but it is old and it is a kit lens) or the Nikkor 50mm f1.4 EI-S for tabletop shots and no one has ever complained about the quality of the prints from these combinations (even easier if the work will go to the www). I have the more expensive Nikon 17-55 f2.8 G ED-IF which, of course, produces better images but to see this difference you need either to look at a 100% crop or really have a difficult light situation, shot against the light, completely open etc.
I think too many people (myself included) spend too much time on the net and too little actually taking pictures.
GLF
For a non-professional, or someone not shooting critically, buying used is a great way to keep money sunk into cameras low. I've done this with the last few dslrs I've owned, and been pretty happy. That said, on the balance of things you probably don't gain an awful lot. With an used camera, you are probably buying it 18 months- 2 years after it was introduced, and also giving up the warranty you would have if you bought now. Against that, you are sinking less money into the camera, which is always nice with a quickly depreciating product.
I've gone both routes myself. I bought a D200 new for €1350, kept it for 3.5 years, and then sold it for €500. In other words, 3 years of useage for €850, along with the benefits of the newest technology, and the associated guarantee on the body. On the flipside, I bought a D300, the next model, just 12- 15 months ago, for €700. Will very well keep it for 3.5 years also, and sell it when I am ready to move on, and am not sure I will be able to find anyone interested in a camera with 6 year old technology at that point. Net result €700 for the same level of usage, but with the disadvantage of older technology, and lack of camera warranty.
Buying used can be the right option, but you do give up a few things by doing so.
In any case, the next few years should be very interesting. For me, sensor technology is not too far away from all I will ever need in it. Resolution and high iso performance are there, and the push is now on dynamic range to do the same. Accompanied by the development that AA filters are being left out of more and more cameras, with moiré likely to become a problem solved entirely by software in the future, soon I feel digital will be at the point where I no longer see a need to upgrade for reasons of sensor technology. Those will be interesting days, and feel we are not too far away from build quality and durability determining how long we keep our digital cameras, no longer upgrading to keep up with the tech curve and to gain valuable improved image quality, but rather that our camera actually wore out.
