The D3000 does a reasonable job even as high as ISO 1,600, though as ever it depends upon scene content. Noise starts to become visible in shadow areas as low as ISO 200, but it's pretty unobtrusive until ISO 800. While not quite as good as the Canon alternatives, the D3000's midrange ISO noise performance is pretty good.
While there's obviously--and unsurprisingly-- quite a bit of noise at ISO 1,600, the D3000 retains sharpness and sufficiently suppresses the serious color noise, both of which render high ISO shots from competitors far less usable. (1/60 sec, f5, ISO 1,600, 18-55mm lens).
D-Lighting is fine for snapshots, when you're worried about blown-out highlights or blocky shadows ruining your photos, but as you can see it decreases the contrast even in appropriately exposed photos, making it less suitable for creative work. I'm not sure whether the D-Lighting actually changed the exposure decision or whether the metering was inconsistent, but the shot without adjustment was exposed 2/3 of a stop brighter than the one with D-Lighting (f9 vs. f11 at 1/60 sec, using matrix metering). That said, in general, I found the D3000's exposures to be excellent.
At its default sharpness settings, the D3000 with the 18-55mm kit lens produces reasonably sharp photos, though some of the details (the dust flecks) look a little bit crunchy.(1/60 sec, f6.3, ISO 100, matrix metering)
Like the bulk of its competitors, the Nikon D3000 renders colors that are bright and pleasing, if not terribly accurate. For instance, the red flowers shown here should look less vivid and a little more different from each other than they do.