After using the Tamron lens for a week or so I'm pretty happy with the result. It's no L series - but it fulfills purpose I got it for - it's light, it covers a good range of focal lengths and in it provides acceptable quality images in a range of conditions.
What it doesn't do is have fast auto focus or reliable focus tracking - so no good for action, but that's what I have the L's for.
I switched back to my favorite 24-70mm f/2.8, after a week of using the Tamron, I noticed the difference immediately- clarity, auto focus speed AND the weight of the lens.
Verdict: the Tamron makes a great every day, walk about lens for surveying the scenery that I might want to come back to later with the heavy kit.
Tasmanian based, New Zealand born