As an avid digital SLR photographer, I've had my eye on the new Nikon D300 for a while now. If the specifications are anything to go by, it may convince some photographers to jump ship from Canon altogether (unlikely I know, but stranger things have happened) or new users will be buying Nikons (not Canon, or other make) from the outset.
I started with the Canon 350D, and then upgraded to the newer Canon 400D DSLR last year. You don't need me to tell you it's a fantastic camera and I am very happy with the camera and results, especially if you invest in quality glass.
With the D300 I feel that Nikon have struck a big blow to Canon in the semi-professional photographer market. The D300s feature list alone surpasses those on Canon's top of the range models, the 1D, which can cost as much as 5-6 times more, let alone the mid-range cameras Canon offers. I mean, 51 AF points are better than 9 as found on the Canon equivalent! 51! But in the back of my mind, I always felt there was something lacking with the D300, almost as though it is trying too hard to impress with it's shiny new features, if such a thing is possible for a camera! Looking beyond the features, and based on the many reviews I've seen, I feel that the D300's image quality is not up to the same quality as a Canon DSLR equipped with a quality lens. Canon still beats it on noise control and produces sharper images.
So, I'll be keeping my Canon 400D for a while longer yet and invest in my first L series lens in the near future. In the meantime, I eagerly await news from Canon on their next line up of digital SLRs. Game on.