Simon Joinson has the following conclusion on the JPG photo output quality from both cameras:
It's clear to see that Olympus – as usual – is doing a great job with its out of camera JPEGs, and at a pixel level the E-P1 produces, sharper, crisper output than the Nikon, and the punchier default contrast, sharpening and saturation mean that the results are more immediately appealing. You're not going to see a huge difference at normal magnifications (and turning up the Nikon's rather conservative sharpening evens things out a little), but there's no denying that the little Olympus is giving the D5000 a good run for its money (though again the rather harsh highlight roll-off produces slightly clipped tones at ISO 100).
Lenses used were the Olympus 50mm f/2.0 Telephoto Macro ED on the E-P1, and Nikon 50mm f/1.4G AF-S Nikkor on the D5000.
Nikon D5000 Test at PopPhoto – Not much of a test, but Philip Ryan nails it on who this camera is suited for:
Family photographers who want more power than a basic, entry-level DSLR, but don’t want to step up to a near-pro camera.
Nikon D5000 Review at Photography Bay – Eric:
Overall, I highly recommend the Nikon D5000 to anyone looking for a feature-rich and very capable DSLR on an entry-level budget. There are plenty of great DSLRs on the market – some offer more features and some may be cheaper. Image quality in the D5000 rivals cameras much more expensive than it and, if you buy something cheaper, you’re going to miss out on some cutting edge stuff that only the D5000 offers.
The video function on the D5000 is the closest thing to getting right as a DSLR has done yet. The Vari-angle LCD really makes a big difference with the D5000’s video capabilities. The file format is easy to work with and the 24p video looks smooth and cool.
The review also includes sample and test photos, and video / movie clips.
Canon T1i / 500D vs Nikon D5000 vs Nikon D300 – Ken Rockwell:
If you demand more pixels and count every one, the Nikon D5000 (or equivalent D90 or D300) gives superior technical results from their lack of noise-reduction induced smudging, ability to correct lens defect color fringes and more reliable AF system. If you look at your photos at 100% on-screen, the Rebel T1i images look more like they came from a compact than an SLR.
Nikon D5000 vs Nikon D60 vs Nikon D90: Paul Christensen's Opinion – Quite a lengthy write-up there.
Having shot extensively with the D60 myself, owned and sold the D90, and now proud owner of the D5000, I can confirm that the image quality on the D5000 is at the same level with the D90, and both cameras have better image quality in terms of dynamic range, tonality and low high-ISO image noise than the D60.
Nikon D5000 Digital SLR Review at Electronista – Mark Elias:
Even so, given Nikon's mastery of still images, we'd still opt for the D5000 above the others. Just beware of your own experience. This near-entry Nikon is best if you're simply looking for a higher-quality alternative to a "prosumer" point-and-shoot or as a learning model. Prospective buyers who fully intend to graduate to more advanced shooting may want to consider paying the extra money for a camera with more familiar DSLR features.
Nikon D5000 vs Panasonic Lumix DMC-GH1 – Steve Morgenstern:
While the Nikon D5000 didn't fare as poorly as the Canon Rebel T1i in our resolution testing, sharpness was still a problem when shooting stills with the camera, where the Panasonic GH1 performed well. Both cameras offer articulated displays that pivot for shooting at an angle, but the Nikon's folds down rather than out to the side, which is less practical, especially since we found the extended screen on the GH1 made it easier to shoot steady video. And speaking of video, the Nikon can't shoot at 1080p the way the Panasonic can and lacks the manual controls and continuous autofocus that make the GH1 a video star, albeit an expensive one.
Why the Nikon D5000's maximum flash sync shutter speed is only 1/200th of a second – Thomas Comerford:
Because it has a mechanical shutter, and at shutter speeds above 1/200 the shutter doesn't expose the entire sensor in one go. Instead, it forms a slit that moves across the sensor exposing each part of it in turn. So if you fired flash during a 1/400 exposure, it might show up in the top half of the frame, or the bottom half, or somewhere in between, but never the entire frame.
Nikon D5000 vs Nikon D90: JPEG Image Quality – Reading through Thom Hogan's article titled "D3000 and D300s Leaked–Predictions Updated", you'll find this paragraph:
What looks a bit weak in the expected lineup is the D90. The D5000 is so close to the D90 that the D90 looks a bit strange in this lineup, especially when you consider that the D5000 seems to produce better JPEG image quality than the D90 out of the same sensor.