I am using the old 80-400mm lens and still am very happy with it, using it mainly for concert photography. Since I don't feel the old lens to be deficient, I am reluctant to upgrade.
Better focusing in low light and smarter auto iso are already worth the price of admission! Those are the things that count most for me.
jmmgarza: If you are a very-busy working photojournalist this is the perfect camera. If you are not, other cameras will take excellent pix and don't cost or weigh as much. If I was rich and had money to blow to impress the yokels... this is the perfect camera. Great lenses back up this camera. I have used the Nikkormat, F1 to the D3s. This is a worthy successor. Recently I pulled my Nikkormat out of mothballs to take pix of friends lecturing on photography at UCLA. Fun times.
I am rich and have money to blow and have ordered this camera today! My only gripe is the fact that maximum regular iso is still 12'800, I hoped this would be bumped up with the d3s successor. I shoot a lot of low light concert photography, so let's see how the sensor holds up at high isos.
I have been comparing images from the Fuji x10 with the Fuji x100 on the 500px.com site. Despite some nice images with bokeh and good conrtrast from the x10, this camera cannot touch the x100 or any other camera with a bigger sensor, so the dream to get top-notch quality in a small package remains unfulfilled - but this had to be expected, the law of physics are the way they are, and the x10 cannot overcome them either.