Photography Blog has posted a review of the Nikon D7000 and the ISO performance is fantastic. It has a multi-stop advantage over the Canon EOS 60D and appears to outperform the 7D by a full stop as well. Incredible performance.
That being said, it still doesn't reach quite as high as some full-frame cameras. In their sample images folder, they have an excellent test of dynamic range, resolution, and ISO in the form of a mall with a large skylight covering the walkway. There is a large difference between the D7000 and the D3x or Leica M9. Yes, there is a huge price difference between those cameras, but I mention it only to remind everyone that all of the technical wizardry in the world hasn't made up for the physical reality of a smaller sensor.
I'm only somewhat invested in the Canon universe and Nikon's stellar work in the past two years has made me consider selling my Canon gear in favor of Nikon. My only reason for not making any moves is that, I think, either company could, at any point, surprise the world by releasing a whole bevy of updated lenses. As it stands, both Nikon and Canon have been rather lax in releasing new lens designs, and after seeing the shockingly good results that can be had with completely new lenses like Olympus' digital Zuiko, better lenses, especially prime, is way more important than updated bodies.
This is especially so, today. The Nikon D7000 provides pro-level results, but only with good lenses. Without great lenses, the difference between this camera and older cameras will be nearly non-existent, if not entirely so. This means that, as bodies get better and cheaper, it will be ever-more required of users to invest in lenses to see benefits, which locks them ever-tighter to a particular system.
This is why all of my money is going into Micro 4/3's. It's a system being built from the ground up that costs so little that if I decide to abandon it, after selling the equipment, I'm out a comparatively small amount. The Zuiko lenses are stellar, stellar, and the Panasonic GH2 matches most of the APS-C cameras on the market. Panasonic and Olympus have shown an absolute dedication to bringing new lenses, bodies, and accessories to market.
I'm playing the waiting game. I'm curious to see who pushes first. I'm pretty confident that it won't be Canon or Nikon. I think that it will likely be Pentax or Sony. They're the underdogs who have a lot to gain. Pentax has already blown the medium format world wide open with their $10,000 645D, so why not do something wild in the 35mm market? Sony has Zeiss lenses and a lot of technical know-how, if only they could bring that together.