Yes, I know that sometimes I sound like a broken record, but the D7000 questions popping up in my In Box also seem like a great deal of deja vu.
People seem to believe that a new camera magically makes their photos better. I would say that this is typically not the case, and for many reasons. Here's just a few:
- We're in the age of declining returns. While more megapixels sound great at the simplest level (Act Now! 16 is better than 12! 14 is better than 10!), it actually takes 4x the pixels to double the capture resolution (e.g., to double 12mp's resolution, you'd need 48mp). When you subtract out diffraction impacts, the actual change in measured resolution in the new cameras is relatively modest, about at the threshold of what can be perceived at 100% view. The simple fact of the matter is that many people want more pixels because they have the wrong lens and need to crop more. If you can't see that this problem is more easily fixable by getting the right lens or spending a little more time on your composition, a new camera isn't really going to help as much as you think (and is going to increase your workflow if you're cropping everything after the fact).
- Noise isn't really measurable, it's mostly perceivable. Yes, technically we can "measure" noise, but the measurements you see posted all over the Internet are mostly meaningless. You can have the same noise measurement from two cameras and one will simply look better than the other to most viewers. Beyond that, luminance noise isn't all that objectionable in the first place, and Nikon bodies have long been good at banishing color noise. One of the primary drivers of "I want better high ISO capability" is again using the wrong lens. If you're using a kit lens that's at f/5.6, you're two stops worse than you'd be with the f/2.8 fixed lens. The latest cameras aren't two stops better than the last generation. You may be better off buying the right lens than a new camera.
- Your images should already be better than film quality. There hasn't been anything wrong with DSLRs for some time (I'm tempted to say going back to the 6mp cameras, but certainly since the 12mp generation). I've long preached that if images you print at the maximum size of a desktop inkjet (13x19") aren't good, then it isn't the camera that's the issue. The problem is how you set it or used it. When I say that, the claim usually becomes that newer camaras should set themselves better. Really? In what way? Exposure in Nikon bodies has always been quite good (and you D80 users only had to move to center-weighted metering and learn to use that, so the exceptions haven't been all that problematic). We've had Active D-Lighting and other "magic" settings in our DSLRs for awhile now. No, it's the gross user errors that people are expecting to be fixed, but people who aren't willing to fix those themselves probably shouldn't be using DSLRs--they're buying a lot of buttons and controls for nothing.
This isn't to say that there aren't people who should upgrade. (Yes, I too had to read that sentence a few times to make sure the double negative was right ;~). But you have to be realistic about what it is that you're getting by updating. I'll take marginal improvements over no improvement any day, but if I had to pay for them directly, I'd be skipping generations along the way. For example, a D40 user moving to a D3100 will likely see quite a bit of meaningful difference. A D3000 user moving to a D3100 is going to see far less.
But the hype now surrounding the D7000 seems mostly to provoke the following quandry in people's minds: D700 or D7000? If you don't already know the answer to that question, my guess is that the D7000 is the camera you should get ;~). I'm going to go out on a limb a bit here: buying into a DX system or an FX system is a bit like buying into either Canon or Nikon. You need to be happy with the ecosystem surrounding the system, not just the body itself. The notion that you'd buy a D700 instead of a D7000 only because it has lower noise (or that you'd buy a D7000 instead of a D700 only because it has noise properties that are "close enough") is a fallacy, short and simple. Need wide angle tilt-shift? Then DX isn't your answer. Need smaller, lighter, less expensive equipment? Then FX isn't your answer.
I don't like "mixed" DX/FX systems for that very reason: you end up duplicating ecosystems (lenses in particular, but often other things like chargers, batteries, remotes, and so on).
So, if you're a DX user, you have to evaluate the D3100 or D7000 as they sit amongst other Nikon DX bodies, or you need to evaluate whether you should be using DX or FX. Once you know that answer, choose the best camera in that format. It's that simple.