As far as optics are concerned, even at wide open (f2.8) the images are sharp corner to corner. You can notice some chromatic aberrations around the contrasty edges at f2.8. For instance you will notice some purple fringing around the edges if you shoot an object against the bright sky. Anyway if you don't shoot against the sky you should have no trouble using it wide open. Personally I only use this lens at f2.8 as the quality of the images is great. The images below are shot at f2.8. You can notice the shallow depth of field and the great bokeh. It has the smoothest bokeh out of all the lens I've used. The optics also have superb resolution.
|nikon 180 @ f2.8|
|nikon 180 @ f2.8|
The only downsides of this lens are its weight and the lack of AF. You have to give it a little time if you want to get a clean focus on the eye (when shooting a portrait), so that the model should be a little patient.
I should mention that the focus confirmation light is not very helpful. Looking at the focus confirmation light while shooting doesn't work for me. I tried out entry level Pentax cameras and they also have a beep focus confirmation alongside with the confirmation light. The audible focus confirmation makes much more sense while composing a picture rather than have another thing to look at. So the lack of the audible focus confirmation is not the greatest feature of the nikon D90 body. On the other hand the viewfinder is pretty big and this is helpful when focusing with this lens.
Compared to it's performance the lens can be bought pretty cheap. Having no electronics and being all metal and glass, there is really very little that can go wrong with this lens.
It's good to have it around in the woods as you can hurt a bear with it, but than you have to also be willing to carry around another 880 g.