Google some info about the D5000--there's lots out there. I've heard different things about it. I've read that this camera (and the D90) were brought out for their video components, rather than for still photography.
I have a Nikon D100, D70, and D60. The D60 can do practically all that the other Nikon DSLRs can do--and more than some!!! Of course, it can't do video. The body is smaller and lighter, which makes it great for the field. The only thing the D60 doesn't have is Auto bracketing for Exposure Compensation--though you can do it manually.
I believe that your lenses have a lot to do with the quality of your images if you have a good basic digital camera that has A, S, and M, modes on it. Check out some of the images here that people have taken with the D60 and some taken with the more expensive (what's considered above an "entry level" camera) and you'll see what I mean. I've seen not so good photos shot with the top of the line cameras, and spectacular ones shot with the D60.
The photographer has a lot to do with it. A mediocre tennis player can buy a tennis racket that a champion tennis player uses, and it won't do a thing for the mediocre player's game.
There's talk of Nikon coming out with a D400--an upgrade to the D300--but so far they are only rumors. There are some Nikon user forums out there.