Although the Nikon version of this lens has been out for a month or so, Tamron recently released the Canon mount version and I had a chance to try it out today at my local dealer.
I did not have a chance to shoot anything with it but I was able to handle it. Although quite lightweight in construction, it's very solid with both smooth zoom and focus controls as well as very quiet VC (Vibration Control). On a Series 1 camera, focus was very quick, and it seemed to lock onto subjects quickly.
Honestly, I'm waiting for Canon's new 70-300mm L (due out at the end of October) but I plan to compare images made from both of these lenses. If the Tamron is as good as some claim, it could be a true "L" killer! Will the Canon be worth $1K more? I look forward to the comparison...