I have a D100, a D70x, and a D200 all of which I love. When the D300 came out I really didn't think that it would be that different than the D200 and therefore I would not upgrade. But after playing with one I could see where the D300 really did make sense for my shooting style and type of photography. I love it. Last weekend I spent time at Chase Field shooting the Arizona Diamondbacks versus the Colorado Rockies spring training game. I had the D300 and my daughter was shooting the D100. This was the first time I've really had those two cameras on the same shoot at the same time. She was struggling a little and asked if we could trade cameras for a half inning so that I could check to make sure the D100 was working correctly. Looking back I am not sure that wasn't a ploy by her although she did have some conflicting menu settings that were causing her problems. While the D100 felt great and the controls were in a natural position for me (discounting that no one makes a left-handed camera), I really missed the advanced metering of the D300 and the larger LCD makes it so much easier to check out photos in the field. The real clincher though was the noise reduction. There are some areas of Chase Field that can be filled with shadow requiring the use of a much higher ISO. The D300 performed light years ahead of the D100 (pun intended). There was just no comparison. So for me the D300 was an invaluable upgrade that I am really happy I made. Like Geoff_M, my former favorite camera (in my case the D200) has been relegated to emergency back-up camera and I shoot almost exclusively with the D300.
Not necessarily on topic but related, I took the D300 with a 70-200mm f/2.8 VR lens on Friday to cover the Diamondbacks vs. Rockies. This is my typical lens for the work I do. I was lamenting that this particular lens was making it impossible to shoot some of the new features of Chase Field (in particular the new JumboTron since I could not fit it in the frame from any vantage point I could find). After cursing that I chose to pack light rather than bring a secondary lens I decided that I would try something different at the next game. On Saturday I was back at Chase Field for the Arizona Diamondbacks vs. Monterrey Sultanes (Mexican League Champion) game. For this game I took the 18-200mm f/3.5-5.6 VR lens just to see what would happen. The extreme wide angle was great for panoramic shots of the field and was especially helpful for shooting the new high-definition JumboTron but once the game action began the lens just was not fast enough even at high ISO to be my primary lens. So as much as I hoped that I could get away with packing light it looks like I'll be carrying my bag with the 17-55mm f/2.8 and the 70-200mm f/2.8 and I may pick up a 1.7x Teleconverter for catching the reaction of people in the stands that are beyond what I can reach with the telephoto zoom. I'm still happy with the 18-200mm and I can still see where that would be a great walk around and vacation lens. But if anyone is looking at one for sports photography no matter what the sport, that lens may be a challenge if you find yourself shooting in low light or need more depth of field control.