Nikon 12-24mm underexposure/focus problems?

I have recently ventured into the world of wide angle with the purchase of a Nikon 12-24mm lens. I have never shot wide-angle before so I have been surprised at some performance behavior with the lens. I have had the following problems and was wondering if it is my inexperience with this type of lens or if there is a problem with the equipment:

- Almost all shots are slightly underexposed, irregardless of the lighting conditions, aperture, or focal length. I am using matrix metering on a D70. I have had to use +1 exposure compensation almost all the time. Exposure is generally superb with other lenses that I have which are the 70-200 f/2.8 VR and the 35-80mm kit lens.

- Autofocus seems to be inaccurate past a couple of feet. Autofocus on subjects within a few feet seems to be accurate, however if the subject is further away the subject has been out of focus in most shots. Landscape type shots have been fine, however if there is an object/person to focus on within the composition, I have had difficulty getting sharp focus on that object/person.
- Sharpness. I understand that due to the nature of the lens, there will be some softness, particularly at 12 mm and apertures at both ends of the scale. However, I used a tripod and wireless shutter release to do some test shots of my Christmas tree, at various apertures and focal lengths, and none of the shots were very sharp.

I have read in other forums about people getting "bad" lenses and having to try 2, 3, 4 or more versions of the same lens to get a "good" one, but I find it hard to believe that Nikon's manufacturing processes would be so poor as to crank out that many defective lenses.

So...I could use some advice feedback on whether this is just the nature of this type of lens. I rarely blame the equipment, but in this case I'm not sure.

Thanks