Just purchased this lens and it's going back. It's beautiful, sharp, great bokeh, but the focus is very in consistent. I blame it on the VC. I tried shooting with both on and off and the pics with the VC off are most consistently sharper than with the VC. Such a shame I wanted to love this lens, but the focus just doesn't cut it. I hope Tamron can address these issues in the future. I love the black look of the lens.
Man that sucks. I do think you have to let the VC kick in before taking the shot. It isn't as instant as the Canon version. I know personally I haven't had that issue, but that could also be due to the fact that I primarily shoot portraits with it and have the time to let the VC engage.