Tamron 17-50 VC first impressions

I received the Tamron 17-50 VC that I ordered from Amazon (it even arrived one day early).  Unfortunately the lens I got was not focusing properly -- specifically, it was backfocusing behind the target (i.e., further away from the camera).  For what it's worth these are my first impressions:

• Build quality seems pretty good, subjectively speaking.  Noticeably heavier than the 28-75.
• The field of view at 17mm (25.5mm equivalent) is impressive.  In this sample shot, I took the shot of our shower from the opposite corner of our bathroom, about 11 feet away.  The field of view was wide enough to capture the wall facing the shower.

Given the wide field of view of this lens, I'm pleased with having chosen this lens over the Tokina 12-24.  I think it will take a while before I feel the need for a "real" wide angle lens.

• Barrel distortion at 17mm is quite noticeable.  Note: barrel distortion (which results in straight lines becoming curved) is different from perspective distortion.  The barrel distortion was not so easy to eliminate in post processing.  Paintshop Photo Pro X3 has barrel distortion correction but I could not correct the barrel distortion completely without introducing pincushion distortion at the borders.

Uncorrected image:

Partially corrected image:

• Resolution: When I first took sample shots the lens, it looked shockingly soft (compared to my 28-75), even at high shutter speeds.  I have since found a photozone review of the Canon version of this lens, with amazing resolution (at least at the center).  This caused me to suspect that there was something wrong with the focusing.  I took dozens of test shots, comparing it with my 28-75, and confirmed beyond doubt that the 17-50 I received had a focus problem, which was not great, but at least kept my hopes up for this lens.  Hopefully the replacement will not have that issue. 
  Given the focus problem on my sample, I would caution potential buyers to make sure they buy from a seller with a warranty (Tamron will not honor its warranty on a gray market item).
  
• Image Stabilization ("vibration compensation (VC)"): This was my first lens with image stabilization.  I previously had a Pentax K100D that had built-in image stabilization, which I found quite effective.  Sample shot from K100D (handheld, 170mm (255mm equivalent), 1/30 sec., 1600 ISO, all ambient light):

In contrast, I wasn't very impressed with the image stabilization of this lens, although in retrospect I think the softness was due to the focus problem, not camera shake.
I also found the sound of the VC working somewhat strange -- it sounded kind of clunky, not a high-tech whirr or buzz that I was expecting.  It's not something that bothers me though.

I look forward to re-evaluating this lens when I get a replacement.

Update: I received a replacement for the 17-50 VC.  It focused identically with the first.  Meanwhile, I upgraded my D80 to a D300.  Strangely, with the D300, both samples of the 17-50 VC focused correctly on the D300 (without micro-adjustment).

2nd update: Here are some real world shots with the 17-50 VC.

3rd update: Here is my 3-month evaluation of this lens.