I use a Nikon D300. I have an 18-135 zoom that was the kit lens from my previous camera (a Nikon D80), a Sigma 10-20, and a Nikkor 50mm f1.8.
As for the results, I do think I get better results from this camera in the sense that it lets me do more of the things I want to do more easily than my previous camera bodies, and it does produce better images overall than the others did. I have owned an N6006 film camera, and a D100 and the D80 prior to this; the D300 is easily my favorite.
That said, I shoot lots of HDR, and while the D300 is the best of all those for that purpose (because it allows me to auto-bracket up to nine exposures), it would be even better if it allowed more customizable control. I'd like to be able to have the camera shoot exposures longer than 30 seconds (because I shoot lots of HDR after nightfall) without having to resort to presetting the remote cable-release timer feature, and I wish I could set the bracketing to vary by two stops rather than just one. I have to shoot by varying by one stop, but I usually process only the exposures that vary by two stops. Therefore, if I shoot nine exposures by auto-bracketing, I have four shots that are wasted. A shutter won't last forever, and I'd prefer not to snap the shutter pointlessly. It seems to me that these are relatively simple software issues, and there's no real reason a user couldn't or shouldn't have this control.
But those relatively minor gripes aside, I love my D300. A real upgrade from this camera would cost a lot of money, and there are still capabilities of the D300 I haven't tapped. For example, I've never shot with Live View. I can't see in low light as well as I once did, and sometimes I have problems composing shots for HDR when the light gets low. Also, reading the LCD on top of the camera is difficult at night, even with the backlighting feature turned on (I think a different method of backlighting might help; maybe the same technology used for Timex Indiglo watches would work well). I think my next project will be to see if Live View will help me with both these issues.
Sorry to turn this into a blog post -- once I got started I couldn't stop!