There is a great deal of competition among camera companies and modern technology is constantly changing so that camera (and particularly camrea sensors) are changing all the time. That being said, in many cases there are few "practical" improvements moving from one camera to the camera that replaces it the following year. Still, so many of us insist on following the idea that "newer is better" and so the push to regularly replace cameras continues and the value of existing cameras drops like a rock. I started to pay attention to this a few years ago when I noticed that my old Olympus E-1 (a FANTASTIC camera) had a used value of less than $200. I was reminded again recently when I was able to buy back a used Nikon D2X (that I sold several years ago for $1,450) from the guy I sold it to for just $300! That's right, I bought a gently used professional grade Nikon DSLR for less than the price of a refurbished D3100! Sure, part of me is happy that we can find such INSANE deals on quality used gear, but another part of me says this is just WRONG. Older cameras like the E1 or the D2X (as long as they don't have any component failures from old age) are as capable of capturing a great image today as they were when they were new and people raved about how awesome these cameras were. More to the point, I just read two different posts on Mu-43 and Dpreview from people complaining that cameras announced within the last 6-12 months have "old sensor technology" and "aren't good for (insert your type of photography here)." Why have we bought into the idea that a new sensor is the most important element of a camera? I feel like the crazy depreciation of digital cameras is a symptom of so many photographers getting sucked into the marketing hype around new cameras and believing the NEED (not "want" or "desire" but NEED) to upgrade exists.