The 105mm f/2.8 Micro-Nikkor is one of our personal favorites. It's on the big and clunky side, and doesn't focus terribly quickly (it depends on the focus motor in the camera body, rather than on a fast "Silent Wave" motor in the lens itself, but its optical characteristics are just so good that we can forgive its minor shortcomings. In fact, stopped down to f/5.6 to f/8.0, this is the lens that we use for all our resolution tests of Nikon-mount digital SLRs. (We also love macro photography, a task this lens is specifically designed for.)
When it came time to put the 105mm f/2.8 to the torture test in our lab, we were pleased to see that its performance lived up to the impressions we'd gained through personal experience. Even wide open, sharpness is on the good side of average, and quite uniform over the entire frame. Dropping down just one stop to f/4 improves sharpness a fair bit, and the "sweet spot" extends from there to roughly f/11, with the best sharpness around f/5.6. Like many lenses though, images from the 105mm get soft when you stop it all the way down to its minimum aperture of f/32. Chromatic aberration is on the low side of average, with a maximum value of about 0.03-0.4% of a picture height, and an average aberration of roughly half that, across the full aperture range. Exposure uniformity is truly excellent, dropping from a worst case of 1/4 EV at f/2.8 to less than 0.1EV at all other aperture settings. Geometric distortion is an almost imperceptible 0.04% pincushion.
No two ways about it, the Micro-Nikkor 105mm f/2.8 is a fantastic lens, particularly if you're into macro photography. While it's in a good focal length range for use as a portrait lens, it's probably too sharp for that usage. (But just a slight blur filter applied in Photoshop(tm) could quickly take care of that.) It's probably not for everyone, but if you want a supremely sharp, high-quality lens in this focal length range, you can hardly do better. If you're a macro shooter, this is a superb tool, with the added benefit of a comfortable working range, thanks to its 105mm focal length.