Had the D3000 been spec'ed to include the 12 megapixel DX CMOS sensor I probably would have jumped for one for my younger daughter. I know from personal D200 experience the 10 megapixel CCD sensor is a great one for people and lower ISO, but it doesn't make as good an all-around sensor as the CMOS one for my usage.
Attraction of these smaller cameras for me is a comparatively very small form factor (I would jump for an 18-55VR to go with) for times when I don't want to carry Dnnn series. Therefore a D5000 makes a good alternative camera when you are going to carry one smaller camera (although it is not as small as a D3000). But not so great as a second camera to a D300 for the reasons Neil cites. So depends what usage you intend to make of the D5000. If you could sell D200 buy D5000 for nearly a wash, I might be inclined to say jump for it for sensor reasons and sacrifice the control differences.
Best regards, SteveK My Nikonians gallery 'A camera is an instrument that teaches people how to see without a camera.' -- Dorothea Lange