I have recently purchased the new nikon D300 and the accessories needed to use it.... I use to have a Sony DSC R1 (a very good camera for the money i paid for it) and the difference is incredible...
Everything is so professional on Nikon, the ISO values is incredible (between 100-6400), the white balance is working so good even on automatic, when you hold it in your hands you really feel like a pro.
I paid around 3000 dollars, on the new equipment but it does make all the money.
If you are in doubt for buying one, dont be... it is truly a very professional camera.