So, I've been asking this question for a rather long time. It was of real concern to me when I was considering a new Olympus body because I thought that I might jump ship. At the time, the D300/D300s was a good performer but a bit old in image quality and there wasn't enough difference between it and the E-5 to jump ship. The D7000 was good but it didn't seem enough in many ways (although it's a great budget body), especially over a used D300.
Now, it's 2013 and the D700 has been replaced and has a cheaper relative in the D600. The D5100 has been surpassed, as well. The D7000 has dropped in price to the point where it's a very good choice...for last year.
I've been expecting a switch and I mentioned in the past with the D600 having been on the way that Nikon might just combine the D7000 and D300s replacements into one body, at a very desirable price point. I'm sure a lot of things delayed the company's progress--a huge earthquake and tidal wave, flooding, and the mirror-less revolution in Japan.
I would hope to see such a camera body soon, given the pricing. Can they combine a better low light experience with a higher image quality for a great price? I believe so. Could the sensors be a problem or are they re-engineering the body to avoid dust and oil contamination, as with the D600 problem?
I'm still unwilling to put US5000 or more into jumping ship, so I'm thinking about it all very carefully. I'm also waiting to see what solution comes from Olympus this year to replace the E-5. Even if it's merely the E-M5 sensor in the E-5 body (coordinated, of course), that would be fine with me. Working at double the ISO image quality would be quite a boost. When Nikon is only stating an upper limit to their working range as ISO 6400 that sounds good, but do I want to use those images?
Any time now...
Update: Well, that was almost one week until the D7100 to be announced. It combines the best parts of the D300 into the D7000 body, and even has an extra crop mode to give Four-Thirds users like me, an easy way to jump ship and get the same 2x multiplication of focal length with a bit of a boost in burst shooting speed. Well done!