Mine's (Serial # 00008xxx) gone back!
I started to notice that the hit rate on focusing wasn't as high as expected and sometime the lens wouldn't lock before the opportunity was gone (even after +8 MA at 24 and 70 mm).
Then a few times the lens would get pinned past infinity focus, jerk back to infinity and then turn out again to the past infinity focus end of travel; this cycle would repeat 4 to 6 times. This occurred more at 70 mm versus 24 mm and usually within the first few shots of usage. This focus issue also occurred with the VC off.
Fortunately the lens acted up exactly this way on a demo body when I was at The CameraStore and they credited my purchase back to me as they didn't have another Tamron lens in stock plus I didn't want the hassle of having to send a lens back for warranty repair within 2 weeks of purchase.
Now the question is another Tamron 24-70VC versus the Canon 24-70 MK II. Even for more $ I'm leaning towards the Canon if it has quicker more accurate focus as I'm using the lens for dance recitals, etc. so focus speed and accuracy is important in lower light and I'm shooting at way faster shutter speed than 1/(2x Focal length) on a 7D so VC/IS/OS has now become a tiebreaker point with me as opposed to a neccessity.
I hope to see some reviews on the new Canon 24-70 Mk II in the near future prior to acquiring another lens in this focal length range.