I really wanted to love the 24-70L, but I often had difficulty getting tack sharp photos without a tripod. I used to lean all over the place just to get a steady shot in low light.
I really wanted to love the 24-105L, but I often felt the speed of F4 a bit lacking. The shutter speed often dropped too low in low light situations to keep subjects still.
Anyway, here comes the tamron to save the day. The VC works fanstastic and at 2.8 and I've been able to take pictures indoors without a tripod or even thinking about finding a good place to lean against.
The build quality is quite good, not quite up to the L lenses but the zoom action is quite smooth and feels nice in hand. There's a zoom lock button, but I've had no problems with zoom creep.
Image quality is excellent. The lens is very sharp in centre and borders are good even wide open. I've heard other's comment that the bokeh is rubbish. But its quite subjective and I find it quite pleasing.
Now if only canon can make the 24-70 III IS.