YES
just retired my D300 when the 800E arrived Friday,, all I can say is WOW,,
I shoot all the grandkids sports (soccer, volleyball, basketball & track) and my hobby of radio controlled one meter sailboats,, many of my boat photos need a fair crop as ya cannot walk out on that water to get closer and the 12 MP D300 ran out of pixels pretty quick,, was blown away at the detail I still had left on cropped photos from yesterdays sail,,
using a 70-200 VR1 the focus is almost instant and the 3D tracking I would rate excellent for the one day of boat coverage I just shot,, as others have said the DR is way above the D300,, can pull those shadows up and see "clearly" items the 300 would never have offered,, colors seem more vibrant but the amount of detail you can see most likely assist,,
I have large hands and the front grip on the 800 is a tad smaller,, will be buying the bottom grip as I had one on the D300 and it never came off,,
I shoot raw all the time and the files sizes will surprise you but hey it is a 36.3 MP camera,, knowing I had ordered the 800E the beginning of February I started looking for a new tower as the old one was a tad over three years and one of my daughters was bugging me about upgrading as the kids always pick up my old gear,,
new tower is i7 processor with one gig video board and 16 gig ram,, it eats through the files very quick on Lightroom 4.1 or Nikon NX2,,
I'm anxious to have a few large posters up to 16X20 printed and can't imagine the quality they will be,,
the D300 supported me very well for several years but I always said if Nikon ever comes out with a high MP camera, no AA filter and a decent price they would get my check,, well they received the check and so far the honeymoon is great,,
Derry