I had ploughed thru all these long threads about this lens before getting one myself. Thought of posting this to assure others about a few things:
(a) QC problems may be exagerated -- I tried a few at the shop, all OK - tack sharp. Maybe the manufacturing process has been tightened up after all the bad publicity. Lens certainly feels more solid than the 18-70mm kit lens.
(b) Focusing -- fast enough for me, no worse than, say the Nikon 50mm f1.4 D lens, perhaps even faster. Also, not any more noisy than the D lenses. (Of course, not as quiet as the AF-S series).
(c) Focusing accuracy -- no problem on a D70.
(d) Vignetting is visible at f2.8 across all focal lengths.
(e) 17mm is wonderful -- although just 1mm less than the 18-70mm kit lens, the angle of view is so much wider.
(f) Chromatic aberration -- a bit more pronounced than the kit lens, but not enough to derail all its other good characteristics. Those who can't stand this will have to get the expensive Nikkor glass.
(g) Image quality is good -- images are sharp corner to corner even at f2.8, although stopping down to f4 or 5.6 provides significant improvements. Most importantly, the lens is usable at f2.8 -- a bit soft, but very usable. I guess, this must be one big reason for its popularity, in addition to its sharpness.