Nikon has introduced the D3100, a replacement for the D3000 and a direct competitor for Canon's Rebel T2i. Most importantly for readers of this blog, the D3100 is the first Nikon DSLR that can do full 1080P video, albeit only at 24fps (faster frame rates require 720P.) It's also got continuous autofocus in video mode, which only the Panasonic GH1 and G2 have been able to do.
Update, August 25, 2010: The first expert feedback is coming in, and according to EOSHD.com, Nikon Germany has stated that the D3100 has no manual controls in video mode. While this makes it easier for first-time users and is useful for some applications, it makes the video mode almost useless for more serious production work.
In Zacuto's DSLR shootout, Nikon's D3S had the best low-light performance but took a backseat in most of the other tests due to being limited to 720P. The Nikon D3000 has nowhere near the extended ISO exposure range of the D3S, but it's an indicator that a professional-level 1080P DSLR is coming from Nikon.
One of the most impressive features of the D3100 is its price: With an 18-55mm zoom lens, its list price in the U.S. is $699.95, almost exactly $200 less than the T2i with a comparable 18-55mm lens. For those photographers who already own Nikons and have an investment in Nikon lenses, the D3100 means that they can move into video without losing their investment.
Before you go rush out and buy a D3100, you should wait until experts such as Philip Bloom and Nino Leitner and blogs like Digital Photography Review have a chance to test it. Resolution is just one of the many factors affecting video quality and performance, and we don't yet know what compromises Nikon made in order to get to the D3100's low price. Nevertheless, the D3100 is proof that Nikon is taking video seriously and intends to keep up with Canon.